Abstract: Aiming at the characteristics of large air leakage area and wide air leakage channels in the side section of the goaf in the goaf under the no-pillar mining in the cut-top stayed roadway, taking the Y type ventilation in the cut-top stayed roadway in Duerping coal mine as an example.The CFD software is used to numerically study the air leakage flow field, air leakage volume and air leakage oxygen concentration of different porosity of the air leakage material in the side lane of the retaining lane.The research results show that the leakage of the working face towards the goaf will increase with the increase in the porosity of the porous medium, and the amount of air leakage will increase.As the distance to the lower corner increases, the amount of air leakage will decrease sharply→parabolic rise→linear decrease→approaching the retaining lanes increased sharply again; as the porosity of the porous medium increase, the leakage from the retaining lanes to the goaf became larger, and the length along the working face increase, and the leakage from the retaining lanes to the goaf gradually decrease;as the porosity increases, the leakage oxygen concentration also gradually increases.