Abstract: Large liquid hydrogen spherical tanks need to be pre-cooled before they are put into service to avoid damage to the tanks from excessive thermal stress, and the pre-cooling process will consume a lot of cold energy, so a reasonable pre-cooling method is the key.This paper takes a 2 000 m³ liquid hydrogen spherical tank as the research object, establishes a three-dimensional numerical model, adopts the liquid nitrogen/liquid hydrogen graded pre-cooling method, and analyzes the influences of inlet flow rate and pre-cooling medium on the temperature drop rate and the changes of the physical field inside the tank during the pre-cooling process of the spherical tank through numerical simulation.The results show that the temperature drop rates at different inlet flow rates followe the same trend, all of which peaked at the 2nd hour of pre-cooling and then decayed. Adopting small inlet flow rate as the initial pre-cooling flow rate, and adjusting the inlet flow rate in time to maintain the temperature drop rate at 3 to 3.5 K/h, the medium consumed to complete the pre-cooling is less and the pre-cooling is more uniform. In the first and middle stages of liquid nitrogen pre-cooling, the highest and lowest wall temperatures occur at the upper and lower sides of the spherical tank, and in the late stages of liquid nitrogen pre-cooling and throughout the liquid hydrogen pre-cooling phase, the highest and lowest wall temperatures occur at the top and bottom of the spherical tank. Due to the wall temperature field, the maximum thermal stress during pre-cooling occurs at the top and upper right of the spherical tank, and it is recommended to focus on monitoring the stress in this area. In the late pre-cooling stage, there are several small, slow-moving vortices in the flow field of the tank, and the overall temperature drop rate in the tank is basically unchanged.