Considering the mutually interacting phenomenon of such aspects as trajectory, orbit and system, this paper designs a suitable trajectory and presents a mathematical model of system/trajectory/orbit integration design and optimization for the small-sized multi-stage solid rocket. By adopting Adaptive Simulated Annealing, Hooke-Jeeves direct searching method, Multi-Island Genetic Algorithm, Successive Approximation method and Directed Heuristic searching method, a major/trajectory/orbit integration optimization for a multi-stage solid rocket is performed aimed at 300 km LEO, and then the optimization results of the five methods are compared with each other. According to the results, here comes to a conclusion that: the model of integration optimization is reasonable; parameter optimization of major design integrated with trajectory optimization digs out the vehicle's merit to a great extent; what's more, the optimization has great effect on vehicle design, and the liquid fuel consumed in orbit-transfer is decreases by 12%. The models and the software can be generalized to the scheme demonstration and conceptual design of other solid rockets.