Here's what could end Apple's winning streak

Apple's share price has been on a tear this year, but perhaps the company has come a little too far too fast.

During the last year, the tech giant's stock price has soared more than 50 percent and on Tuesday the company's market capitalization reached a record $700 billion. But now the lingering question is how long can the momentum last?

Read More Apple's market cap hits $700B, doubles under Cook

"The stock has done really well, largely from the fact that the iPhone 6 and iPhone 6 Plus have been a big success for these guys. So the question is how far can this keep sustaining?" said Amit Daryanani, an analyst at RBC Capital Markets.

And while it's difficult to find an analyst on Wall Street who is bearish on Apple, even those who have a "buy" or "outperform" rating on the stock see some perils for the company.

Read MoreAt new highs, Apple only starting to ripen: Analysts

Here's a look at some risks that bullish analysts are watching.

Missing iPhone expectations

Apple's iPhone sales account for more than half of the company's revenue. And because the new iPhone 6 models feature significant hardware and software updates, it's widely expected that the upgrade cycle will have legs well into 2015.

Wall Street estimates Apple will ship more than 60 million iPhones in the first quarter, according to StreetAccount. One estimate by the well-connected KGI Securities analyst Ming-Chi Kuo even projects iPhone sales will reach 71.5 million for the holiday quarter.

Optimism about the potential for a longer upgrade cycle even has analysts setting the bar high for iPhones sales well beyond 2015. But perhaps they have set the bar too high.

"The big concern I see is not being able to live up to the huge expectations they have now," said Louis Basenese, founder of Disruptive Tech Research.

"They had a great launch of the iPhone 6 and the estimates are very aggressive for unit volumes. It's a contrarian indicator, but the analysts now are extremely bullish and their revised price targets are already underwater and you get concerned it's come a little too far too fast and you look at what causes shares to correct and I think it would be missing expectations for unit volumes," said Basenese, who is long-term bullish on Apple.

Another fear is that iPhone sales could hit a wall in 2015 because of its success rate, RBC's Daryanani said.

The iPhone is on track to capture almost 70 percent of the high-end smartphone market ($300 or more) in the next few months, at which point the company could possibly face some market saturation concerns, said Daryanani, who has an "outperform" rating on the stock with a $120 price target.

"If you are looking at having 70 percent market share in the next few months, you have to ask where is the new opportunity or where are the new revenue drivers for them?" he said. "So you have a hit point where you run into some saturation in the market. In the next six months this could become an issue."

Competition in China

While many analysts expect Apple's expansion in China to continue to be a catalyst for iPhone sales, increased competition from smartphone makers who sell at a lower price point could pose a threat to the company's success in the region.

Read MoreApple locks in key partnership in China

"China is the single-biggest swing factor. But it's also the largest untapped opportunity," said Alex Gauna, an analyst with JMP Securities.

While China's growing wireless infrastructure means more smartphones in the region, it doesn't mean the iPhone will be the dominant player.

Gauna, who has an "outperform" rating on Apple's stock with a $135 price target, said that some Chinese handset makers, like Xiaomi, are doing very well and that could pose a threat to the iPhone maker.

Read MoreChina's Xiaomi makes strides in smartphone race

"Xiaomi has been very, very successful. So they could have the potential to create the same headache that Samsung created for Apple two years ago," Daryanani said.

Apple Watch sales

While Wall Street is hopeful that the Apple Watch will be a new revenue generator, the company still runs the risk of weak consumer adoption.

"I think the Watch, does it really become the next product for them or is it just a cool accessory? They need it to be the next product, a new category for them. If it's not, if it doesn't become one like some of the other smartwatches out there, that's a downside risk," Basenese said.

Poor battery life, not enough use cases and high price point are just a few of the things that could also deter consumers from purchasing the device, industry experts said.

"It's probably the use cases and the battery life. Why does one need to go out and buy an Apple watch, suddenly having a product that needs to be charged every day? It's not the most convenient thing," Daryanani said.

Still, though, Daryanani said that he estimates Apple will begin selling the devices in March and will sell 20 million units at an average price of $520 in 2015. In total, he predicts that Apple Watch sales will come to $10 billion in additional revenue and 40 cents in earnings per share. Given that the Apple Watch is only compatible with models of the iPhone 5 or later, though, he said estimates should remain conservative.

Besides adoption of the watch, investors should also be keeping an eye on how well Apple Pay fares, Basenese said.

"If traction isn't significant right out of the gate, they are going to be playing catch up. Apple will have to explain why they aren't getting more adoption," Basenese said. "They have the credit cards on file, they have the smartphones in peoples' hands, there are plenty of places where consumers can use it. Explaining why they don't have traction, would become a significant problem."

Apple did not immediately respond to a request for comment. Still, the company seems confident of its chances for success. CEO Tim Cook said during Apple's last earnings conference call that demand for the iPhone 6 is "off the charts." He also said that "we are heading into the holiday season with Apple's strongest product lineup ever." And "we are also incredibly excited about the Apple Watch and other great products and services in the pipeline for 2015."

Apple also predicts that it will sell more products in the three months leading up to January than it did in all of 2010.