The problem of multi-robot cooperative localization based on relative bearings is researched in this paper. Relative bearings of different robots are fused with motions to improve the localization accuracy of robots. We analyse the situations about relative positions of the robots and their motion trajectories. Some relative positions and motion trajectories of the robots easily lead to not-converged localization results. We present an improved method to overcome the fault. The robust and practicability of localization are greatly increased. Simulation results prove the method is effective in dealing with the cooperative localization problem.