In order to study the effect of nanoparticles on the thermal conductivity of base oil,nano diamond particles with different volume fraction and particle size were added into castor oil,and the particle number density,radial distribution and thermal conductivity of the particles were studied by using the method of LAMMPS and molecular dynamics.The results show that the thermophysical properties of nanofluids with nanoparticles are affected by many factors,including concentration,size of nanoparticles.With the increase of the volume fraction of nanoparticles,the thermal conductivity of nanofluids increases approximately linearly.With the decrease of the size of nanoparticles,the loadcarrying capacity of nanofluids is increased.The lubrication film formed by nanofluids has a high bearing capacity,which helps to reduce friction and improve surface wear.The lubricating oil with nanoparticles can reduce the friction between the friction pairs,enhance the heat dissipation and improve the thermal conductivity.