In recent years,the ACDCAC transmission methods have been deployed ubiquitously in the highspeed trains, the grid voltage fluctuation and even instability becomes more frequently which willaffect the safe operations of these equipment. The previous study found that the stability of the power grid will be sufficiently impacted when highspeed trains are in the regenerative braking mode.In order to realize the regenerative braking energy recovery of the traction converter, and to ensure the stable operation of the cascade system between the power grid and the traction converter.In the nonideal power grids, the cause of the stability problem is derived based on the impedance analysis in this paper. The joint simulation verification is conducted among the Simperer, Maxwell, RMxprt, Matlab/Simulink platforms. The results show that improved parameters can overtly reduce the oscillation in the cascade system, and hence enhance the train operation reliability.