Abstract: Based on the simulation of linear PLL,this paper puts forward an improved method to analyze and simulate the nonlinear performance of PLL.Some PC-based circuit CAD programs (such as IsSpice,Pspice,etc.)can be used to model the nonlinear PLL,as a illustration,one instance with sine PD and step frequency hopping is simulated with this method,from it we can watch the locking process of a PLL circuit which is impossible for a linear PLL model analyses,further more,a magic phenomenon can be found to determine whether it will lock out.