The invention discloses an elastic return-difference-free 3Z planetary reducer. The elastic return-difference-free 3Z planetary reducer comprises a central sun wheel, planetary wheels, planetary wheel shafts, a planetary frame, a fixed inner gear, a rotating inner gear and a bearing and is characterized in that a layer of elastic material is additionally arranged at the matching position of each planetary wheel shaft and a hole, a layer of elastic material is additionally arranged at the matching position of a sun wheel shaft and a hole, one planetary wheel is adjusted to enable the central distance between the planetary wheel and the sun wheel to be smaller than theoretical value, the central sun wheel is eccentrically placed on a shell of the fixed inner gear, the corresponding central distance between each planetary wheel and the fixed inner gear is larger than theoretical value, through elastic material deformation, the central sun wheel, the corresponding planetary wheels, the fixed inner gear and the rotating inner gear are tightly engaged, and no side gaps exist.