: The problem of micro-pressure waves caused by trains entering the tunnel from the open line becomes increasingly prominent,due to the increase of train speed. Relevant studies show that the combined type hood can better mitigate the impact of micro-pressure waves than the single type hood. In order to further mitigate the impact of micro-pressure waves on the surrounding environment of the tunnel, this paper proposes the combined type hood with step openings. Based on the two-equation turbulent flow model and the numerical simulation method, the initial compression wave pressure and pressure gradient caused by the train entering the tunnel are analyzed in detail from four aspects: the opening distance,the opening rate, the number of opening holes and the opening position. The hood has small impact of the maximum pressure of the initial compression wave, and the difference of the maximum pressure value is kept within 10Pa, which has great effect on the pressure gradient of the initial compression wave. When the opening distance is 4m, the opening rate α is 36%, the number of opening holes is 2, and the opening position is the top opening, it is the optimal working condition, and the pressure gradient mitigation effect reaches 60.14%.