In this paper the desorption kinetics of volatile in condensed mode polyethylene process is studied through experiments. It is found that though the residual volatile in particles at the later stage of desorption accounts for a relatively small portion of the total quantity, the desorption of this part of volatile requires much longer time than at the earlier stage. For high requirement of devolatilization, the total time needed will be predominately determined by the residual amount of volatile in particles. Temperature has greater effect on the desorption rate than other influence factors, especially in the later period of desorption. A model is proposed to calculate the volatile desorption rate for condensed mode polyethylene process.