Aiming at the problem that the measuring results of wrist force sensor can be influenced by load end’s attitude change when mechanical arm moves，this paper proposes a load gravity compensation algorithm for wrist force sensor. According to gravity variation of the load end in different mechanical arm posture，the relationship between the gravity of load end and the position of the center of gravity can be measured by experiment. We build a wrist force sensor gravity compensation model，and combining manipulator kinematics equation，we deduct a load gravity compensation algorithm for wrist force sensor and a calculation method for force acting on the end of mechanical arm. Specific examples have been tested by adopting the ADAMS and MATLAB joint simulation method. The results show that this compensation algorithm can effectively eliminate the influence of the attitude change of load end，the external force information of mechanical arm can be measured by wrist force sensor. And the results verify the correctness of the load gravity compensation algorithm for wrist force sensor.