A lubrication system includes an engine oil pump, a lubricating oil tank, a breathing pipe, a machine body, and an oil pan. The engine oil pump is formed by superposing upper and lower layers being a lubricating pump and an oil return pump. An oil inlet of the oil return pump leads to a cavity of the oil pan, and an oil outlet leads to an interior of the lubricating oil tank. An oil inlet of the lubricating pump leads to the interior of the lubricating oil tank, and an oil outlet leads to a machine filter. The machine filter is communicated with a main oil path of the machine body. An oil tank cover of the lubricating oil tank is provided with a breathing one-way valve and an oil filling port. The breathing one-way valve communicates one end of the breathing pipe, and the other end thereof communicates a crankcase.