Every year, the widespread use of natural gas in buildings results in a number of accidental gas explosions. On December 7th, 2015, a gas explosion accident occurred within buildings in the Shijingshan District of Beijing, China. Three people were slightly injured when a flammable concentration of natural gas had accumulated in the enclosed building space and ignited, resulting in a gas explosion. To study the process of this explosion and its destructive effect, a physical model that was consistent with the actual event was firstly established, using accident data from the above accident. Windows and doors in the building were designed for pressure relief. According to different leakages and scopes, numerical simulation of gas explosion was carried out by computational fluid dynamics explosion simulation software. In the simulation, the finite volume method was used to solve the compressible N-S equation in the three-dimensional Cartesian grid. In this paper, the shock wave propagation process in the building was analyzed and typical blast-wave curves were plotted at different locations. By comparing numerical simulation results with actual event, the most consistent filling scheme and equivalent ratio of gas reactions were obtained, and the calculation showed that the overpressure field and temperature field were consistent with the actual scene. Simulation results agreed well with actual destruction in the accident and verified the validity of the scheme. This research can provide suggestions for evaluating injuries and damages when gas explosions occur and might help in anti-blast designs and accident investigations. (C) 2017 Elsevier Ltd. All rights reserved.