The utility model discloses an oil supply device of a Roots blower. An oil outlet is formed in the bottom of an oil tank. Four layers of oil filter nets are arranged between the bottom of the oil tank and the position above the oil outlet, an oil pump is arranged at the position below the oil surface of an oil pool, the oil tank is provided with a lubrication state observation window, and the diameters of meshes of the four layers of oil filter nets are sequentially reduced from top to bottom. The oil supply device of the Roots blower has the advantages that the oil pump is arranged at the position below the oil surface of the oil pool, so that the phenomenon that oil cannot be obtained when more air exists in an oil pipe is avoided; the oil tank is provided with the lubrication state observation window, an operator can observe whether lubrication oil quantity is sufficient or not in real time, and lubrication is added in time so as to ensure continuous running of the Roots blower; the four layers of oil filter nets are arranged to filter out impurities in the oil tank, and the problem of blockage caused when the impurities enter an oil path pipeline is avoided.