Abstract: A numerical study was performed for physical field of liquid hydrogen horizontal tank based on CFD technique and the distribution of temperature field,velocity field and tank pressure changes were depicted.The appearance and cause of thermal stratification phenomenon were analyzed.It is found that heat transfer of liquid hydrogen is convection and the convection boundary layer was formed between the tank wall and the hydrogen liquid.The thermal stratification appeared along the gravity direction,and the profile of the liquid hydrogen is Gauss probability curve.The flow in the tank is a unsteady and the location of vortexes changed continually.The self-pressurization phenomenon of the tank is obvious and the curve of the self-pressurization is nonlinear.