According to tribochemical reaction and modeling of action mechanism ,the action mechanism optimized by nanoparticles in oil lubricating under friction is studied .The surface of a couple material is optimized by the together action of three approach stated as follows: Firstly, the thickness and intensity of lubricating layers or films provided with the action improving tribological properties increase because of enrichment of nanoparticles on the surface or near surface of couple-material arising from short force. Secondly, new lubricating film is built because of tribochemical reaction concerned with nanoparticles enriched in surface under friction and wear. Thirdly, the surface of couple-material is optimized by nanoparticles, for instance machine polishing, filling and leveling up the tiny hole and crackle on surface.