The present invention relates to a gear reduction method. The gear reduction method comprises the following steps of installing a gear input mechanism at the eccentric position of a rotating body which does not have an output rotating shaft, driving the gear input mechanism to carry out revolution around the axis of the rotating body by utilizing the rotation of the rotating body to thereby enable the gear input mechanism to obtain the rotation kinetic energy from the eccentric position of the rotating body; using a gear output mechanism to carry out deceleration processing on the rotation kinetic energy transmitted by the gear input mechanism and then output outwards. According to the present invention, the output rotating shaft on a motor rotor is canceled, so that a gear reduction unit manufactured by utilizing the method of the present invention has the technical effects of compact structure and small occupied space.