A dynamic trajectory planning algorithm based on vehicle steady-state dynamics for driver assistance systems (ADAS) under high dynamic environment is proposed. The algorithm built a 'search space' on the basis of traffic vehicle trajectory prediction and used the vehicle steady-state kinetic model as a trajectory generator. Every trajectory produced by the generator was evaluated in the search space and the optimal trajectory under optimal conditions was selected. In order to realize the closed-loop dynamic simulation, the corresponded trajectory tracking algorithms and vehicle dynamics model were also proposed. A simulation platform under Simulink environment was built for simulation tests. The results show that in the intelligent overtaking test case, the proposed algorithm is able to overtake safely and to meet the needs of intelligent assistance systems.