A hierarchical trajectory planning method with path and speed co-search and decoupling optimization is proposed to address the multi-constraint trajectory planning problem in structured road scenarios. To ensure the quality of the initial trajectory solution, the upper initial trajectory planner constructs the Spatio-temporal cost map by taking into account the risk field and spatio-temporal information of dynamic obstacles, and searches for the safe and feasible initial trajectory using a three-dimensional A* algorithm. The lower trajectory planner implements decoupling for the trajectory planning as path planning and velocity planning with the minimum curvature, maximum speed, and comfort as the goal. A numerical optimization algorithm is used to construct a spline optimization model for the path and speed, in order that in the process of obstacle avoidance it can give full play to the dynamic performance of the vehicle and at the same time improve the ride comfort, simplify the constraint conditions on local space-time tunnel thought, and improve solving efficiency. The experiment results show that the proposed method has better driving efficiency, comfort, and real-time performance.