Numerical investigation on flow process of vortex valve controlled SRM was carried out. A three-dimensional numerical model was established to simulate internal flow field of variable thrust SRM based on vortex valve. By experimental validation, it was concluded that the model was agreed with test data to some extent. The steady and transient numerical simulations were performed. The swirling flow character in vortex chamber was revealed and the relation between vortex property and SRM thrust modulation capability was obtained. The results provide information for variable thrust SRM design and performance analysis.