A nutation reducer, to solve a problem that a knuckle bearing adopted in existing nutation reducers to perform nutation movement is complicate in structure, its volume is large, leading to low power density. A nutation reducer in this application includes: a case, two pairs of nutation gear pairs, each pair being disposed in the case and composed of a nutation gear and non-nutation gear in engagement, and the non-nutation gear being fixed in the case or integrated formed in the case; an output shaft, rotationally disposed in the case; two annular spring films, each nutation gear of the gear pair is connected to the output shaft through one annular spring film; a nutation generating mechanism disposed in the case, two nutation gear pairs being respectively disposed on both sides of the nutation generating mechanism. Power-split arrangement is applied in this application, symmetric layout of the nutation gear pairs is adopted. In this way, the working efficiency of the reducer is obviously improved, meanwhile the volume and weight of the reducer, and the heat generated in working process are reduced, and power density is improved.