The utility model relates to an oil leakage prevention device used for a fan bearing box. The oil leakage prevention device used for the fan bearing box comprises a ball valve, a first pressure gauge, a pressure stabilizing valve, a one-way valve, a filter, a second pressure gauge and a shell. The ball valve is connected to the first pressure gauge through a pipeline, the first pressure gauge is connected to an inlet of the pressure stabilizing valve through a pipeline, an outlet of the pressure stabilizing valve is connected with an inlet of the one-way valve, an outlet of the one-way valve is connected to an inlet of the filter, and an outlet of the filter is connected with the second pressure gauge. All the parts are located inside the shell. According to the oil leakage prevention device, pressure, generated due to temperature and rotor rotation, inside the sealed bearing box is eliminated through a series of valve adjustment; the situation that a fan shaft which rotates at a high speed squeezes out lubricating oil due to pressure is avoided, wherein the lubricating oil is splashed on the diameter of the shaft or the position of an end cover of the bearing box and the phenomenon that oil leaks outside is also avoided accordingly.