The utility model discloses a pneumatic grease filling device which can fill grease for mechanical equipment in a pneumatic mode and is very suitable for filling grease for an oil pumping unit in the oil industry. The device comprises a grease gun, a grease cylinder and a pneumatic motor. A grease chamber connector of the grease cylinder is connected with the grease gun through a grease flexible pipe. An air cylinder chamber connector of the grease cylinder is connected with the pneumatic motor through an air inlet flexible pipe. Grease is injected into the grease gun through the pneumatic motor and the grease cylinder, and manual force is not needed. When grease injection is achieved for oil pumping unit maintenance through the pneumatic grease filling device, the pneumatic grease filling device improves working efficiency, reduces working intensity, is convenient to operate, and improves safety factors.