In view of the working requirements of the gear shaping machine, the double crank-crank slider mechanism is designed for the main transmission mechanism of the gear shaping machine. A multi-body dynamics model with joint clearance of the double crank-crank slider mechanism was established, and the motion simulation was performed. The slider motion characteristics were studied with the different sizes clearance on the joint and the different positions of joint clearance. The results show that: the slider speed characteristics become worse with the increase of the clearance at the same position, but the slider displacement curve is unchanged. Both the displacement and speed of the slider were affected with the same size of joint clearance at different positions; the largest amplitude of slider speed fluctuation was produced with the clearance at the E joint, and at the same time the slider stroke was increased, the maximum speed of the slider back was lag, but the value was increased. The results can provide a reference for the designing of the main transmission mechanism of the gear shaping machine.