The invention discloses an engine piston assembly, and relates to automobile engine piston assemblies. According to the engine piston assembly, a pressure relief groove is formed below an oil storage tank, the pressure relief groove, the oil storage tank and a lubrication groove located in an inner cavity of the oil storage tank all communicate with one another, and the stress concentration of a piston pin boss is reduced, so that the risk that the pin boss is destroyed is reduced; and a sharp corner structure and a semi-circle protrusion are arranged on a second gas ring, and the lubricating effect is enhanced. According to the engine piston assembly, a nasal type sharp corner is arranged on an oil ring, the airtightness and the oil-scraping effect are enhanced, and the engine piston assembly has the advantages that the airtightness is good, the air leakage is low, the power performance is good, the structure is simple, machining is convenient, and the cost is low and reduced.