Simulation speed is a noteworthy issue in the simulation of continuous system. Although previous research has to some extent obtained some achievements, it is still very slow for complex system simulation. A schematic diagram is formulated to describe and analyze the simulation process of continuous system in SimPowerSystems environment. Three simulation methods are proposed based on different ways of discretization mathematical model, namely continuous method, discrete method and hybrid method, and their implementation approaches are presented as well. Meanwhile, the characteristics of modules in Simulink and SimPowerSystems are also studied. Simulation performance of three methods are illustrated by theory analysis and case verification, the results show that discrete method can obviously improve simulation speed. And when sampling time is 5us, discrete method meets precision requirement generally. It has important significance for the simulation of large system.