In order to achieve real-time and accurate measurement of the force between the end of the bionic finger and the object being grasped, this paper establishes a motion model between the bionic hand and its end effector, with this proposed mathematical model of it, the grasping force and moment of the bionic finger can be calculated. And then, a spatial resolution measurement method of force sensor based on the motion model is proposed and described. We evaluate our method by several experiments, the results show the effectiveness of this method. With motor motion control method, the bionic hand with a force sensor can grasps an object like humans.