In order to study the effect mechanism of copper nanoparticles on the increase of thermal conductivity of ricinoleic acid base fluid,based on molecular dynamics simulation (MD) method,the influence mechanism of thermal conductivity of nanofluids was studied by taking the diameter,adding amount,shape,Brownian motion and system temperature of copper nanoparticles as variables.The results show that the Brownian motion of nanoparticles can improve the thermal conductivity of nanofluids.The addition of Cu nanoparticles changes the density of some regions of ricinoleic acid based fluid,and the resulting liquid adsorption layer hinderes the thermal conductivity.The thermal conductivity of nanofluids is increased with the increase of nanoparticle diameter,adding amount and system temperature.At the same size,the nanoparticles with a large surface area can increase the thermal conductivity.