A rotary joint actuating device of robot is designed combining the screw transmission mechanism with the crank-slide mechanism. Firstly,with the software Solid Works,the three-dimensional model of the rotary joint is built. Based on the motion analysis,the mathematical model of the rotary joint is established,the rotational range of the end-effector is got. Then,the theoretical output torque of the end-effector is taken as object function,the relationship between the output torque and the rotation angle is analyzed to further verify the rationality of the parameters design. At last,the experimental prototype is made,and the angle measurement scheme is presented for the rotary joint. An electrical test platform of the rotary joint is set up. The test results show that the motion range of the rotary joint is larger and the effect of its mechanical transmission is good.Also,the rotary joint is easy to control and its structure is simple.