In order to warn drivers of rollover threat states of semi-trailer and control the states in time,the current motion states of semi-trailer were estimated in real time by using Kalman filtering technique.Meanwhile,we treated semi-trailer in TruckSim as a real vehicle and took the process noise and measurement noise into consideration.Then a TTR (time-to rollover) rollover warning algorithm associated with model prediction was established by determining vehicle lateral load transfer rate as the rollover threat index.In addition,through combining with optimal control algorithm,anti-rollover control strategy was developed based on TTR rollover warning algorithm.Simulations show the proposed control strategy can warn drivers effectively of the dangerous situation,and control rollover threat states of semi-trailer to prevent rollover.