The W/O microemulsion was prepared using rapeseed oil,Span 80,TX-7 and butanol.CaCO3 micro-nano particles were in-situ synthesized by microemulsion as microreactor.The characterization of CaCO3 particles shows that the CaCO3 particles change from globular to fusiform with the increase of water content,and the size of CaCO3 particles can also be controlled by water content.The tribological behaviors of the CaCO3 micro-nanofluid were investigated by four-ball friction tester.The results show that the friction coefficient of the microemulsions is reduced by about 55.74% compared with the base oil,and the CaCO3 particles increase the maximum non seizure load of the micro-nanofluid by about 10.88% and reduces the roughness of the friction surface by about 16.01%.The laminar reversed micelle has small shear stress and is parallel adsorbed on the friction surface under the action of surfactant,so it has excellent antifriction effect in the process of friction.The fusiform lamelliform CaCO3 particles can isolate the direct contact between the asperities of the friction surface and reduce adhesive wear and abrasive wear.It can improve the surface quality of friction surface and the extreme pressure performance of the lubricant.