The invention relates to the field of processing of cycloidal gears, in particular to a cycloidal gear tooth profile correction method, a cycloidal gear and an RV (rotary vector) reducer; a main operating area of each tooth of the cycloidal gear is located mainly between the root and crest of the tooth close to its middle, and the root and crest are non-principal operating areas. The method of the invention imparts a second-order or higher-order parabolic relationship the correction amount of the tooth profile and a normal distance from a standard cycloidal gear node to a meshing point of a standard cycloidal gear and pin wheel, the correction amount decreases gradually from the crest and root to the middle main operating area, a certain meshing clearance is generated in the non-principal operating areas and forms a lubricating clearance, and the main operating area has small correction amount so that it is ensured that the main operating area attaches to the standard cycloidal gear tooth profile to the maximum extent; during transmission in no-load state, only one pair of teeth are involved in meshing transmission; after loading, the cycloidal gear and the pin wheel deform slightly under stress, multiple pairs of teeth are involved in meshing, meshing contact ratio is increased, and the transmission is more stable.