Abstract: The effects of operating parameters, such as steam load, circulation ratio and water level, on the performance of curved-arm steam water separator for steam generator of CANDU6 reactor were calculated and analyzed by computational fluid dynamics（CFD） technology. Euler two fluid model and three sizes of the water droplets, which were 100 μm, 200 μm and 300 μm respectively, were used to simulate the two-phase flow of steam and water in the separator. Results show that the influential trend of operating parameters on separation performance is basically identical for all the three droplet sizes, the droplet size independence law applies. When the droplet size is 300 μm, more accurate separation efficiency and pressure loss value can be obtained. As the steam load is increased, the separation efficiency increases and the outlet humidity decreases, while the circulation ratio and the water level result an opposite influential trend. The pressure loss increases as steam load or circulation ratio increases, but the pressure loss coefficient decreases, the influence of water level on pressure loss and pressure loss coefficient can be ignored.