A miniature device for automatically filling lubricating oil is composed of an oil storage device, a pump and an oil filling mechanism. The oil storage device is composed of a spring, a cylinder, a piston, and an oil filling filter, wherein the spring is sheathed on the piston rod, the piston rod protrudes out of the cylinder cap at the end portion, the oil filling filter is arranged on the lower portion of the cylinder, and an oil outlet hole is formed on the bottom of the cylinder. The pump is a plunger pump and is composed of a base, a pump body, a plunger, a plunger base, a check valve, and a dispenser, wherein the base is fixed on a rotation shaft supported by a lubricating component; the pump body is arranged on the base; the inlet of the plunger pump is connected with the oil outlet hole on the bottom of the cylinder; the check valve at the outlet of the plunger pump is connected with the dispenser which is connected with the component to be lubricated; and the plunger is connected with the plunger base. The oil filling mechanism consists of a connection rod mechanism and a bevel plane, wherein the connection rod mechanism is composed of a rolling wheel, a push rod, a rocker, and a pin, which are connected with each other; the push rod is a hollow rod; a reset device is arranged in the hollow rod; the rocker is connected with the plunger base; and the bevel plane is connected with the rolling wheel at the front end of the push rod.