For dynamic satellite communication systems with adjustable user coding and modulation modes, if the coding and modulation mode selected by the user is inappropriate, the bandwidth will be limited when the system allocates resources. In order to solve this problem, the system allocates modulation and coding modes according to the actual business needs of each user, and improves the utilization efficiency of system resources through the joint allocation of power and coding and modulation modes. This paper first analyzes the links of satellite communication systems, considers the construction of a mathematical model for the joint allocation of power and coding and modulation modes, and proposes a hybrid gravitational search and particle swarm optimization algorithm to solve this problem. In order to improve the performance of the proposed algorithm in the constrained objective optimization function, a dynamic inertia weight coefficient is introduced to avoid the algorithm from falling into the local optimal trap, and a penalty function mechanism is added to process the constrained objective optimization function to achieve the optimization of the objective function. The final simulation results show that compared with a single particle swarm optimization algorithm or a gravitational search algorithm, the hybrid gravitational search particle swarm optimization algorithm designed in this paper reduces the total second-order service rejection of the system and effectively improves the total capacity of the system.