Abstract: Traditional research on automatic lane change has primarily focused on high-speed scenarios and has not considered the dynamic state changes of surrounding vehicles. This paper addresses this problem by proposing a trajectory planning method to enable automatic lane change at medium and low speeds. The method is based on a dynamic safety domain model, which takes into account the actual state change of surrounding vehicles, as well as the upper boundary of the safety domain for collision avoidance and the lower boundary of comfort for vehicle stability. The proposed method involves the quantification of the safety and comfort boundaries through parametric modeling of the vehicle. A quintic polynomial trajectory planning method is proposed and evaluated through simulation and testing, resulting in improved safety and comfort for automatic lane change.