Abstract: A approach was proposed to solve multi-phase trajectory optimization problem. The approach allowed the trajectory for hypersonic vehicle in vertical plane dividing into several phase, then obtained the multi-phase trajectory optimal value by collaborative optimization method. Only the transitional phase, gliding phase and descending phase were investigated. The expectation was that the terminal velocity maximum in transitional phase, the range maximum in gliding phase and the flight time minimum in descending phase. The three phase was regarded as three discipline, and the attack angle and initial condition were as input and terminal condition as output for every discipline. The collaborative optimization software coplatform was developed to solve the multi-phase trajectory problem. The result is identical with the one obtained by all in one method or globle sensitivity equation(GSE) method. It also shows the collaborative optimization method is effective to solve the multi-phase trajectory problem.