The invention discloses a deburring device for an inner cavity of a shell of a wiper motor reducer. The deburring device comprises a pressure pressing-down mechanism (1), a rotating cutter head mechanism (2), a push broach and product positioning mechanism (3), an electric control cabinet (4), a device rack (5) and an operation panel (6), wherein the whole rotating cutter head mechanism is fixedly arranged at the lower part of the pressure pressing-down mechanism (1) through a cutter head fixing seat (2-1); the push broach and product positioning mechanism (3) is mounted on the device rack (5). The deburring device for the inner cavity of the shell of the wiper motor reducer is provided, at each position where a burr is easily generated when the shell is subjected to compression casting, with a corresponding deburring mechanism; the detection is carried out by using a programmable logic controller (PLC) and various sensors, so as to realize that each action is executed according to a design requirement; the quick and accurate positioning on a part and the deburring of a square hole with large amount of burrs in the shell are realized according to the requirement that multiple positions of the part need to be deburred; a qualified blank is provided for the fine machining of a subsequent procedure.