This paper shows effectiveness of bracing for precise and low electrical energy consumption of the end-effector in the case with and without the constraint of the joint of mobile manipulator. Considering that human can do accurate task with less power by bracing elbow on the table, we believe that manipulators can save energy and do a task more precisely like human by bracing itself. Therefore this paper first discuss the motion equation of robot with constraint condition, and robots dynamics including motor's dynamics also. Then the effects of bracing are analyzed and displayed.