Based on the Neel-Brown relaxation time theory and the effective temperature model proposed by Li et al.，the thermal effect in current induced magnetic spin torque switching is theoretically studied. On the basis of Landau-Lifshitz-Gilbert equation and Fokker-Planck equation，through analyzing the current induced magnetic switching and potential change，a new model to explain the potential barrier reducing is proposed. Different from Lis model，this model is nonlinear. The model is used to discuss the relation between temperature，switching time and critical current. For the current induced temperature rise，our model does accord with the experiment well. The method for determining the intrinsic switch electric current，testing time and intrinsic potential barrier in magnetic switching is also proposed.