At present, there is a lack of study on the destruction mechanism and characteristic in the investigation after gas explosion accident. The destruction and treatment scheme of two accidents happened in Shanghai were introduced. According to the precast slab and poured slab that badly damaged in the two accidents, the anti-explosion ability of the slab was obtained through theoretical calculation and numerical simulation, and then explosion overpressure was estimated. The reason why the overpressure differs little but the destruction differs much in the two accidents and the destruction characteristic of the gas explosion to the building were all analyzed. It is considered that: 1) the anti-explosion ability of the poured slab is far superior to the one-way precast slab; 2) Room with the ignition source is impacted by the overpressure directly and the damage is most serious, while the destruction of the other rooms is caused by the vibration, and its influence is smaller as the house is far from the explosion.