According to a processing method of an MEMS substrate, before the substrate is corroded, a second mask layer and a third mask layer are formed on a side face and a rear face of the substrate. Since the second mask layer can effectively protect the edge side face of the substrate, corners are prevented from being broken at the edge of the substrate due to edge side face corrosion of the substrate while the substrate is corroded. In the following processes, the substrate is not prone to break, and the yield of the MEMS substrate is raised.