Abstract:A simplified method in trajectory optimal design is provided for the coupling question of the ascent phase trajectory and the return phase trajectory. Firstly, by taking the key parameters from the ascent phase trajectory design which affected the range of the rocket first stage, the trajectory of ascent phase is designed. There are two different characters on the separation point of the ascent phase trajectory with the same constrain of the range of the first stage. Next, the launch capacity and the trajectory character is analyzed on different separation point, for return to or not to the launch site. The results show that if not return to the launch site, low trajectory is better than high trajectory, and if return to the launch site, high trajectory is better. The analysis results would provide a reference for the trajectory design of vertical landing reusable launch vehicles.