The Mach 2 hydrogen-air supersonic combustor model without diffuser was designed and tested in atmospheric inflow condition. A new supersonic mixer, which was vent slot mixer (VSM), was developed and confirmed its performance as a mixing device. At low enthalpy inflow condition, plasma jet torch was used as the igniter and the flame-holder. The VSM showed that the interaction between the fuel and the air through the vent spread the fuel to the spanwise direction in the recirculation region. The shock train structure generally depends on the combustion pressure, and the combustor condition becomes the unstart condition with combustion pressure increase. Although the mixer loses its mixing efficiency under the shock train, the VSM shows that it stabilizes the combustion around the vent. Therefore, the VSM has distinct characteristics for the mixing efficiency and the combustion stabilization.