After the municipal solid waste is landfilled, the organic matter in it will degrade and a large amount of gas will be generated. If the gas production rate is too fast or the exhaust is not smooth, the internal pressure will be too high, resulting in deformation and settlement of the landfill body. Based on this, a plane model test of pressure-induced unsaturated soil failure and numerical simulation were carried out to study the soil deformation and failure mechanism under different soil thicknesses and different gas pressure conditions. The results show that: The process of soil damage induced by air pressure can be divided into four stages: water vapor migration, local micro cracks, main cracks penetration and internal cavities; soil damage mainly occurs in the inverted triangle area between the top of the inflatable hole and the surface layer. And according to whether there is a previous gas pressure effect its failure form can be divided into two types: “splitting failure” and “burst failure”. Proper gas pressure is conducive to increase the stability of soil mass. On this basis, the concept of critical stable gas pressure is proposed. The change law of seepage in soil is studied by the proposed numerical simulation method, the results show that the regional change of effective stress increment is the cause of critical stable gas pressure, which can provide a reference for practical engineering.