One disadvantage of the double helix rotary cylinder is that the transmission efficiency of the screw pair is too low. In order to get the value of the lead angle when the transmission efficiency was maximum, the mathematical model was built. Then with the help of VB and MATLAB, the optimum value of the lead angle was gotten. It is indicated when the value of the lead angle is 46.8°, the transmission efficiency is maximum, which is 88.31%.