Abstract: On the ground of general control equations, by paying attention to heat transfer characteristics in thermal entrance region and optimizing relations which affect the heat transfer, such as ones for velocity fields , eddy diffusivities for heat and momentum transfer, the present authors established a calculation model easy to be solved with the help of computer program. With the further simplified conditions, the effect of an axial heat conduction on heat transfer to liquid sodium in thermal entrance region was calculted and analyzed.