As the aerospace vehicle gradually enters the era of refined design, especially for civil aviation aircraft with high subsonic economic cruising and fighters with high maneuverability at transonic speed, the demand for high-performance transonic wind tunnels is becoming more and more urgent, and the numerical simulation of the high-speed section of the tunnel has certain reference significance for the design of transonic wind tunnel. Therefore, an 8.50 plane asymmetric diffuser has been calculated firstly, the separation and reattachment points agree with the experiment; Secondly, the convergence criterion, initial condition and slotted wall divergence angle of high-speed section for transonic wind tunnel have been considered, the results indicated that the mach number of monitoring points in model section has represented numerical convergence. Also, the influence on velocity distri-bution at model section and streamline in slot with different initial conditions is negligible. Moreover, the slotted wall divergence angle 0.3° has acquired more uniform flow fields than divergence angle 0.0°.