There are two popular practical models of synchronous generator used in power system transient simulation,both of them are based on Park equations and can be defined as assumed A and assumed B,according to the different assumptions.In order to study the influence of different models on the calculation precision of transient stability,single-machine infinite system is taken for example to compare the transient stability calculated by two practical models,and the simulation results are verified by time-step finite element model (T-S FEM).The results show that the transient stability calculated by assumed A is close to that calculated by T-S FEM,thus the transient stability limit calculated by assumed A is more accurate.