Abstract: Aiming at the problem that autonomous driving vehicles are prone to rollover and skidding in ice and snow downhill curve scenarios, this study constructs a three-stage braking speed planning model based on the S-shaped curve by analyzing the characteristics of ice and snow roads and the longitudinal and lateral dynamic characteristics of vehicles. This model divides the vehicle braking process into three stages: the deceleration increase stage, the constant deceleration stage, and the deceleration decrease stage, uniform deceleration section and deceleration section, and takes into account the key factors such as the adhesion coefficient, gradient and curvature of three kinds of common icy and snowy roads, such as loose snow, snowboard and ice board, etc., and based on the road information, obtains the safe speed of the self-driving vehicle on different icy and snowy downhill turning surfaces, and adjusts the vehicle travelling speed by the constraint of the safe speed to realise self-driving vehicle Smooth braking. In addition, in order to verify the model validity, the CarSim platform is used to construct different gradient, curvature, and road surface ice and snow road scenarios for simulation verification. The simulation results show that on the loose snow road surface, the maximum yaw angular velocity of the vehicle reaches 0.255 rad/s, the maximum centroid lateral deflection angle is 0.016 rad, and the maximum lateral acceleration is 3.05 m/s². On snowboard roads, the maximum yaw angular velocity is 0.215 rad/s, the maximum centroid lateral deflection angle is 0.028 rad, and the maximum lateral acceleration is 2.14 m/s². On the ice plate road surface, the maximum yaw angular velocity is 0.148 rad/s, the maximum centroid lateral deflection angle is approximately 0.051 rad, and the maximum lateral acceleration is 1.17 m/s². In addition, an increase in road slope and curvature will slow down braking, increase the fluctuation of yaw velocity and centroid deflection angle, and reduce lateral acceleration. On icy and snowy roads with a low adhesion coefficient, vehicle deceleration slows down, yaw velocity and lateral acceleration decrease, and centroid deflection angle increases.