The September surplus with the U.S. was larger than China's overall trade surplus of $31.69 billion for the month.
The world's two largest economies are locked in a bitter trade dispute, with U.S. President Donald Trump taking issue with his country's massive trade deficit against China.
For January-September, China's trade surplus with the United States was $225.79 billion, compared with about $196.01 billion in the same period last year, Reuters calculations showed.
Overall, China's dollar-denominated September exports surged 14.5 percent from a year ago, beating a Reuters analyst poll forecasting 8.9 percent growth in the same period. In August, Chinese exports grew 9.8 percent from a year ago.