The outstanding performance on thermal transport of nanofluids makes it possible to replace the traditional heat transfer working medium in micro heat pipes with nanofluids. The flow and heat transfer properties of copperargon nanofluid under different number of nanoparticles were investigated. The results show that the thermal conductivity of nanofluid in the microchannel is anisotropic. In details, the thermal conductivity of the flow direction (parallel to the wall) is much higher than that of the direction perpendicular to the wall. In terms of flow characteristics, the number density of the base fluid atom near the wall is about 1.7-2 times larger than the average number density, and the velocity of the base fluid near the wall is smaller than the average velocity. What's more, there exists a thin liquid layer near the wall (the thickness is about 3.66×10^-10 m).