The invention provides a grease gun oil feeder which is an equant cylinder; an oil cavity is arranged inside the cylinder and internally provided with a piston, the central part of which is attached with a top plate, and the upper part of one side of the piston is provided with an oil outlet pipe mounting hole; a slat-shaped extrusion plate is fixed at the upper edge of the cylinder of the oil feeder by connecting screws at two ends, a screw rod nut is connected at the central part of the extrusion plate, a screw rod is arranged between the piston and the top plate inside the screw rod nut, and the upper end of the screw rod is connected with a rotary handle; and oil outlet pipes are connected inside the oil outlet pipe mounting hole arranged at one side of the piston and another oil outlet pipe mounting hole positioned on the extrusion plate. In the cylinder of the oil feeder, the screw rod is used for ejecting the piston to form pressure, and grease can be lifted by the pressure andinjected into a grease gun for the use of mechanical oil injection. The grease gun oil feeder has the characteristics of small volume, light weight, convenient use and carrying, sanitation and environmental protection, and is suitable for the application of injecting the grease by using the grease gun.