A four-stroke engine lubrication system comprises: an engine body in which a crank shaft chamber and an air valve distribution chamber are arranged; a cylinder head cover fixed onto the engine and communicated with the atmosphere; and an oil storage tank which is configured to store lubricating oil, arranged on the engine body, located at one side of a cam, and provided with an oil mist generation device therein, wherein an oil outlet passage of the oil mist generation device communicates the oil storage tank with the crank shaft chamber via an oil outlet pipe; the crank shaft chamber is communicated with the air valve distribution chamber via a check valve; the air valve distribution chamber is communicated with the oil storage tank via a pipe; the air valve distribution chamber is communicated with the cylinder head cover; and the cylinder head cover is communicated with the oil storage tank.