Abstract: A special two-stage whirlwind steam separator was designed based on the research of relevant domestic and foreign data, and the detailed numerical simulation research was conducted in terms of its separation performance. According to the structure of the two-stage cyclone separator, a computational analysis model was established, and the separation performance of the separator was calculated by numerical simulation. The effect of different inlet velocity and different humidity on the separation characteristics of the separator was studied, and the air-water cooling test circuit was built to verify the model. The results show that the numerical simulation results are consistent with the cold test results, and the deviation of separation efficiency is small. In the design condition, the overall separation efficiency of the separator is better than 99.5%. The primary separator is suitable for coarse separation, and its separation efficiency decreases with the increasing of inlet humidity and velocity. The secondary separator is suitable for the separation of small droplets, and its separation efficiency is positively correlated with the inlet velocity and non-linear with the inlet humidity.