In order to raise position and posture precision of farming robot, double three-point fix disposition principle and method of farming autonomous mobile robot were proposed which were used to implement position and posture precision of the robot when it was moving independently, and the laser survey sensor and ultra audible sound receiving sensor were employed to build up the measure and test system and realized examination. The experiments show that operation speed and controlling precision are increased by using the methods, its absolute error is aggrandized, whereas its relative error is reduced obviously, and it is sensitive for barrier on the ground, and its stability can enhance by raising its weight.