Abstract: A simplified two-dimensional numerical model of 1:45 was established based on the passive safety system of the passive containment. Under the premise of keeping the dimensionless number unchanged, the Fluid Volume Function (VOF) model was used to capture the gas-liquid interface, and the liquid film spreading conditions under different Reynolds number Re conditions were analyzed. By comparing with the experimental results, the simulation results can better reflect the liquid film fluctuation in the experimental results, and the change of liquid film thickness is consistent with the Reynolds number. The process of vertical wall falling film is synthesized by a variety of forces, the fluid film can be divided into obvious laminar and isolated waves, the bottom flow velocity of laminar flow is low and the solitary wave moves faster along the flow direction, and the collision and fusion between the isolated waves intensifies the fluctuations of the liquid film with the spread of liquid film; With the increasing of Re, the thickness of the liquid film at the bottom layer and the amplitude of isolated wave increased, and the volatility increased.