The invention relates to the technical field of planetary reducers, and provides a planetary reducer and a robot. The planetary reducer comprises a first-stage planetary gear device and a second-stageplanetary gear device, wherein the first-stage planetary gear device comprises a first-stage gear assembly and a first retainer assembly, a first annular channel is formed in the first retainer assembly, a plurality of rolling components are accommodated in the first annular channel, the rolling components make four-point contact with the inner side surface of the first annular channel, and the first-stage gear assembly receives power input; and the second-stage planetary gear device comprises a second-stage gear assembly and a second retainer assembly, a second annular channel is formed in the second retainer assembly, a plurality of rolling components are accommodated in the second annular channel, the rolling components make four-point contact with the inner side surface of the secondannular channel, and the second-stage gear assembly carries out power output. The planetary reducer is small in height dimensions, and light in weight.