The six-month stock market rally is based on temporary measures and could evaporate once government stimulus has run its course, Pimco's Mohamed El-Erian told CNBC.

Mohamed El-Erian, co-chief executive officer of Pacific Investment Management Co.

Combined with a sharp reduction in inventory and cost-cutting, the stimulus has helped move stocks higher though that could all end when 2010 comes and reality hits, El-Erian, co-CIO of the world's largest bond fund, said in a live interview.