91.9％。In view of vibration and loud noise that existed in the course of applying the current ring-reducer, a new type ring-reducer was firstly proposed, which consisted of two-stage transmission, one involute transmission and a planetary transmission of N-type with small tooth number difference. The new type reducer did not only reserve the advantages of the current ring-reducer, but also had the characteristics of smaller volume, bigger transmission ratio and higher stiffness. The principle and structural style of the new reducer have been analyzed, and the power flow has been studied. The relation of angular velocity and the balance equation of torque was deduced, and the transmission efficiency of the new reducer was calculated.