Abstract: This paper derives force equilibrium equations of a robot and presents a method to calculate the driv-ing forces and reactions in all the joints.This method has obvious physical meaning,generality and higheffectivcness.After considering the effect of the links’ weight on the driving forces,an optimum designmodel of relief mechanisms is presented.The calculations are carried out with examples.The results haveshown that the amplitude and the fluctuation of driving forces can be obviously reduced if a relief mecha-nism with optimal parameters is used in a robot.