The invention discloses relates to a photovoltaic solar silicon wafer thinning device and discloses a device for carrying out two-face grinding prethinning on a silicon wafer through two stages of planetary wheel discs. The photovoltaic solar silicon wafer thinning device is characterized in that a sealing bearing is arranged in the middle of the bottom end of a scrap receiving disc, one end of a connection shaft penetrates through the sealing bearing to be arranged in the scrap receiving disc, the middle of a grinding workbench is arranged on the connection shaft through a connection sleeve, the upper surface of the grinding workbench is provided with a liquid guide groove which is of a net structure, the installation groove density in center of the grinding workbench is larger than that in the edge position, multiple rubber rings are arranged on the grinding workbench and distributed annularly, the diameter of the rubber rings is gradually increased from the middle to two sides, the inner wall of each rubber ring is evenly provided with convex points, the grinding workbench is provided with multiple distance limiting holes, distance limiting marker posts are arranged in the distance limiting holes, a first center gear is arranged on the connection shaft and located below the grinding workbench, and a primary planetary carrier assembly is arranged on the connection shaft.