Aiming at the problem of multi robot collaboration mapping, a real-time grid method was proposed. Grid map was created during exploration through controlling robot formations, and the obstacle was located. Using wireless communication and directional infrared ranging technology, the fleet formation was maintained, grid area was divided at the same time. Adapting leader-following method and VHF+ obstacle avoidance method, the formation was controlled to round obstacle. The principle and feasibility of the method were demonstrated. The effectiveness of the method was verified with InnoSTAR robot. This method has simple calculation, and it occupies less storage space, can be realized on small robot with simple sensors, but the relative position of the robot fleet must be controlled.