For the intersatellite communication, the conventiaonal resource allocation does not match the requirement of practical services and the variation of channel conditions, which consequently cannot make full use of limited satellite resource. Nowadays, small satellite formation flying system attracts more attention to its great advantages mainly in reliability, cost, performance, and becomes a promising technology in the field of international aerospace. Intersatellite communication bears the mission of information interaction between two small satellites, the small satellite and relay satellite, the relay satellite and the earth synchronous satellite. Since the power and bandwidth in satellite communication is limited, it is of great significants to improve the utilization of such resources. In this paper, by constructing satellite communication system capacity model, a joint communication bandwidth and power allocation algorithm is proposed under different channel conditions and service requirement with respect to different communication link. Then, the Lagrangian duality theory and the subgradient method is adopted mathematically. With the iteration of the power and bandwidth, respectively, the optimal power and bandwidth can ultimately be achieved. Simulation results indicate that the proposed algorithm can allocate the bandwidth and power resource efficiently, increase the system capacity, and improve the utilization of resources.