Abstract: A computational fluid dynamics program FLUENT is used to predict the fluid flow and pressure change in a zero boil-off cryogenic storage tank for liquid hydrogen storage tank using a two dimensional model in microgravity enviroment. This model consists a tank with cylindrical wall, and oblate spheroidal top and bottom, a heat pipe was located along the symmetric axis of the the cylindrical tank, and a pump nozzle unit was built. The results indicate that the gas bubbles were appeared the top and bottom of the tank, and then their volumes become bigger as the heat flux from surroundings entered. Meanwhile, the maximum temperature and pressure increase gradually. The pump nozzle unit and cryocooler are opened when the pressure reaches the setting value(about 80 hours), the volume of the gas bubble is smaller, the value of temperature and pressure decreases obviously.