The utility model provides an oil tank draining device. A water baffle board is obliquely and upwardly welded along the inner wall of the upper part of the oil tank, a drain pipe is welded at the position where the water baffle board is welded at the outer wall of the oil tank, and a shutter is arranged at end head of the drain pipe. The oil tank draining device is simple in structure, is easy to produce and perform, can have quick effects with low investment, can collect and discharge the water condensed on the top part of the oil tank in a centralized way, can reduce the moisture in the hydraulic oil, can reduce the corrosion on the top part of the oil tank, can ensure the purity of the hydraulic oil, can prolong the service cycle of the hydraulic oil, can reduce the oil emulsification in the oil tank, and can reduce the hydraulic consumption and cost.