The invention relates to a quantitative gear oil filling tool. The quantitative gear oil filling tool comprises an oil storage tank 6, a sealing cover 4, a connection rod 2 and a filling nozzle 10, wherein the longitudinal section of the oil storage tank 6 is in a U shape, the bottom of the U shape is provided with an opening, and the filling nozzle 10 is arranged at the position of the opening; the connection rod 2 is arranged inside the oil storage tank 6, one end of the connection rod 2 abuts against the position of the opening, and the other end of the connection rod 2 extends out of the plane at the top end of the U shape of the oil storage tank 6; and the sealing cover 4 is fixedly arranged on the plane at the top end of the U shape of the oil storage tank 6, the sealing cover 4 is provided with a hole, and the connection rod 2 penetrates out of the hole and can freely slide in the hole. The quantitative gear oil filling tool can achieve quantitative and automatic oil filling, by means of the filling tool, quantitative gear oil is automatically filled every time, the production efficiency is greatly improved, the labor cost is effectively saved, meanwhile, air pressure convection between the tool and the space to be filled can also be formed, and the situation that the gear oil is sprayed out and pollutes the production environment is effectively avoided.