The invention discloses a planetary wheel side reducer assembly. The inner end of a wheel side half shaft of the planetary wheel side reducer assembly is fixedly connected with a steering knuckle, and the outer end of the wheel side half shaft is connected with a sun wheel through a spline. A plurality of planetary wheels which are meshed with the sun wheel are arranged on the circumferential face of the sun wheel, all the planetary wheels are correspondingly arranged on planetary wheel shafts in a sleeving mode, the planetary wheels share one gear ring, and the gear ring is mounted on a gear ring tray. According to the planetary wheel side reducer assembly, the sun wheel, the planetary wheels, the planetary wheel shafts, the gear ring and the gear ring tray are all arranged in a wheel side shell, the wheel side shell is connected with a hub, and the hub is connected with a hydraulic brake disc. The planetary wheel side reducer assembly has the advantages of being low in weight, ingenious in structure, high in precision, small in noise, capable of achieving high torque capacity, longer service life and more reasonable maintainability in a confined space, and the like.