Abstract: To study the effect of filling flow on the filling process of the large liquid helium tank, one-dimensional unsteady thermodynamic model is established for the liquid helium tank, and the different filling flow conditions are simulated and calculated. The simulation results show that the liquid helium filling process is divided into three stages: tank precooling, liquid helium accumulation and tank container standing. With the increase of filling mass flow, the time of tank precooling and liquid helium accumulation stage decreases, the temperature drop rate increases, the time of helium mass and thermodynamic energy peak advances, and the fluctuation amplitude of helium flow at tank outlet increases. The liquid helium filling flow increases, and the filling time exponentially decreases. For a large liquid helium tank with a volume of 20 m³, the recommended maximum filling flow is 20 g/s.