Mathematics model was established on analyzing the sport appearance of two vehicles and the process of braking . it is optimized . and then logical mathematics model was obtained 2 、对本车与前车的运动状态以及本车制动过程进行了分析与研究,建立行车临界安全车距数学模型,并在此基础上进行了误差分析与防撞预警判别修正,得出合理的数学模型。