Abstract: A series of contrast experiments were done to obtain the influence of vertical vane on flow inflexion, the loss of stagnation pressure and cavity static pressure. The cause of influence of the vane on diffuser flowfield is expounded by analysis. The vane can increase the length of supersonic region, the stability of cavity pressure, and reduce the loss of stagnation pressure thus to increase the pressure recover coefficient. The vane thickness has great influence on cavity static pressure, so the thickness must be controlled to avoid coming into being the normal shock.