Fire fighting and rescue activity needs much manpower. Moreover, fire fighters and rescue company members face risky situation. Therefore they are good and suitable subject for robots development. Then, we discuss the effectiveness of accident response robots and rescue robots from its size and configuration. We resulted to that a small mobile robot group is the one of the effective system for rescue robot in accidents. The mobile robots group needs to move from safety area to accident site or danger field first. There has already developed some leading-following system. However there was no consideration for accidental situation and circumstance. Therefore we propose a tracking trajectory planning method that is useful for the mobile robots group against accidents. Furthermore, we carried out numerical simulation to confirm the performance of the method. Finally, we conclude the tracking trajectory planning method that we proposed is useful for small mobile robot group for accident response based on the results of numerical simulations.