The paper proposes a method by grid to constructed the map, here we called “Grid Map”. Our mobile robot installation the ultrasonic sensor to detects environment. Here we list some examples for state the environment for record below: Free space, Occupies space, Un-pass Space. Also, use electronic compass to detect magnetic properties and identify the direction. Therefore, the angle will be compensation when the robot is moving. The grid map is using feature point for clustering feature. And then, generalize feature point in grid of region. During this research, the “Grid Map” is using to solve the problem of high dip to cause the huge statistics, but also can be basis of guidance. To achieve the robot can move arbitrarily in the indoor environment. Therefore, the paper proposes state accuracy and reliability to evaluate.