The present invention relates to a gear reduction unit. The gear reduction unit comprises a rotating body not having an output rotating shaft, a gear input mechanism arranged at the eccentric position of the rotating body and used for obtaining the rotation kinetic energy at the eccentric position of the rotating body, and a gear output mechanism connected with the gear input mechanism and used for carrying out deceleration processing on the rotation kinetic energy obtained by the gear input mechanism and then outputting outwards. According to the present invention, the output rotating shaft on a motor rotor is canceled, so that the gear reduction unit of the present invention has the technical effects of compact structure and small occupied space.