In order to study the working performance of instantaneous venting in a small wind tunnel,the venting characteristics of the wind tunnel were studied through numerical calculation and experiment. The venting model of the wind tunnel was established for numerical calculation. The results show that the pressure in the vessel decreases exponentially and the mass flow gradient in the wind tunnel outlet is large in the process of sound velocity venting; the pressure in the vessel decreases in an approximate quadratic curve and the mass flow in the outlet of the wind tunnel decreases linearly in the process of subsonic venting process. The experimental model was set up in the wind tunnel test section and the venting test was carried out. The experimental results agree well with the numerical results, which verify the correctness of the numerical calculation.