In order to achieve optimal control of articulated heavy vehicles under medium/high speed uncertain conditions, an active trailer steering strategy for articulated heavy vehicles based on mode switching in medium/high speed conditions is presented based on the linear variable real-time parameters simplified model. The active trailer steering strategy is based on trailer active steering. According to different medium/high speed conditions, the different control modes are used to control in the strategy. The aims, which are to control vehicle rollover under the limit condition and to achieve the good path follow,yaw and jackknife stability under the normal working condition, are obtained. In order to obtain the optimal control effect for the different control objectives, the optimal weight coefficients,which are suitable for different control modes, are obtained by the genetic particle swarm optimization algorithm. Simulation study is operated and simulation results indicate that:from low adhesion to high adhesion, from normal working condition to limit working condition, the proposed strategy can achieve good control in medium/high speed conditions.