With the intention of man-made radioactive aerosol separating and monitoring in a high radon environment, in this paper, a novel submicron virtual impactor was developed, and a numerical simulation model was established. Then, the rationality of the numerical method was validated by comparison to experimental data. Afterward, the variations of separation characteristics under different operating conditions of sample flow rate, minor flow ratio and clean air velocity ratio were discussed and analyzed in detail. In view of the different inertia between man-made and natural radioactive aerosol, the proposed novel submicron virtual impactor could provide a quicker approach to separate and detect the man-made radioactive aerosol particles. After that, the collection nozzle structure of the virtual impactor was improved based on the computational fluid dynamics analysis results. The results show that the proposed impactor has a higher separation efficiency and lower wall loss for fine particles compared to the conventional structures.