Abstract: A real time navigation and obstacle avoidance method based on grids for fast mobile robot has been developed and implemented on our mobile robot(THMR-Ⅱ). This method allows the detection of unknown obstacles and avoids collisions while simultaneously steering the mobile robot toward the target in smooth, stabled and continuous motion. Experiment results from mobile robot THMR-Ⅱ traversing obstacle courses demonstrate the effectiveness of the method in typical environment.