Semi-active suspension control is the best solution to current China's high-speed train suspension system. A variety of methods can be used to semi-active suspension control under stationary random excitation. But when the train running at a changing speed, the spatial random irregularity signal will be pulled and pressed to be a non stationary signal in time domain. And because of the randomness of track irregularity, the damper of traditional semi-active control cannot meet the requirements of quick response. In this paper, an open-loop optimal control method is put forward to solve this problem. Firstly a simulation based on a 17-degree-freedom vibration model built in the MATLAB/SIMULINK is done. Then, according to the simulation results, the analysis about the effect of open-loop optimal control on the vehicle lateral riding quality from time domain and frequency domain is made. The results show that the open-loop optimal control can improve the lateral stability of high-speed trains, and the lateral vibration acceleration is also improved in the frequency range between 0.1 and 2 Hz which is sensitive to human body.