For gas leakage explosion accidents that occur in high blockage environments, the failure of building structures often leads to the evolution of explosion waves becoming unpredictable, resulting in the amplification of accident consequences. In this paper, a severe gas leakage and explosion accident in Beijing is analyzed using computational fluid dynamics (CFD) method, and the disasters of the accident are evaluated based on the evolution of physical quantities. The laws of propagation and impact damage of explosion waves based on structural failure are also summarized. Based on the numerical analysis results, the explosion of 4.0–4.1 m³ combustible gas is sufficient to destroy a large number of walls with a maximum indoor overpressure of 1.130 bar and create a high-pressure injury area of 10 m and a high-temperature injury area of 14 m outdoors. The impact behaviours of explosion waves are closely related to the building structures and obstacle characteristics. Structures whose spatial direction is the same as the propagation direction of the initial wave suffer less damage, and similar obstacle characteristics on both sides of structures reduce damage. The disorder of gas explosion intensity leads to the unpredictable failure direction and process of building structures, and the collapse direction of component may be opposite to the path of initial explosion wave; Outdoors, the gas flow rate of several hundred meters and the peak dynamic pressure of 0.5 bar caused all the glass of two buildings to break. Therefore, a reasonable pressure relief area and sufficient safety distance become the key measures to prevent and mitigate the disaster of civil explosion accidents. The research results can provide scientific basis for the investigation and loss prevention of explosion accidents, as well as safety assessments in the process industries.