The main factors affecting the stability of the process of bidirectional beam tracking in inter-satellite optical communication are investigated. The iteration convergence process of the bidirectional beam tracking is analyzed by building the model of aiming error angle which images in the array detector in the receiving terminal, with considering the influence of signal noise ratio. Steady tracking constraint conditions theoretical formula which is closer to the actual situation is deduced. The theoretical result is verified and modified by simulation and the simulation experiments on the ground with optical terminal. The above work has important significance to modify a satellite communication system.