Abstract: A mathematical model of gas-liquid two phase flow is built based on Eulerian-Lagrangian method, and this model is solved by the commercial CFD software CFX to simulate the flow characteristics in an AP1000 swirl-vane moisture separator in a special compression rate under cold condition. In this model, gas is supposed to be the continuous phase and water droplets moving in the separator are thought to be the dispersed phase. According to the motion characteristics of droplets in the flow field, we consider the droplet is controlled by the drag force, virtual mass force, buoyance force and gravity force, and in consequence build the momentum two-way coupling dynamic model of gas and droplets. Aiming at 9 working conditions, we used CFX software to solve this two phase flow model to get the trajectories of droplets with different diameters, in addition to obtain the separation efficiency and total pressure drop between inlet and outlet of the separator. The results show that the computed separation efficiency agrees well with the cold condition experimental data, and the changing trend of the calculated pressure drop is the same as the experimental value, which reveals the correction of our model.