Abstract: This paper reports the extreme pressure antiwear property of combination of three kinds of addtives determined with four ball machine. It has been found that the wear scar diameter becomes smaller when sulfurized alkene and phosphorous-nitrogen additive (or rust preventer) are added simultaneously; the wear scar diameter becomes larger, when both rust preventer and phorporur nitrogen additive are used. When three kinds of additives are combined, their effects on wear scar diameter are in the following order: sulfurized alkene>P-N additives>rust preventer; and those on nonblocking maximum load are in the following order: rust preventer>sulfurized alkene>P-N additives. The interaction mechanism on combination of additives and the relation between element content on the film of wear surface and the extreme pressure antiwear property were studied by IR, ~(31)PNMR and AES.