The invention provides an oil tank cover. The oil tank cover comprises an oil tank cover main body. The oil tank cover main body is internally provided with a one-way valve fixing base. A one-way valve cover is arranged in a groove in the upper end of the one-way valve fixing base. A one-way valve which can move up and down relative to the one-way valve cover and the one-way valve fixing base is arranged between the one-way valve cover and the one-way valve fixing base. The top of the one-way valve cover is provided with a through hole which can be sealed through the one-way valve. A reset spring is further arranged between the one-way valve and the lower end of the one-way valve fixing base. The purpose that gasoline in an oil tank does not make contact with the outside atmosphere under a free state can be achieved; and in addition, external gas enters the oil tank under the working state, and the effect that air pressure inside and outside the oil tank is balanced is ensured, so that an engine runs normally.