Abstract: To meet the needs of numerical simulation of large-scale gas explosion engineering, based on the relationship between laminar flame thickness and initial pressure, the traditional thickening flame model was improved so that the thickening factor could automatically adjust according to local pressure. At the same time, based on the open source program Cantera and genetic algorithm, a multi-component single step chemical reaction model capable of accurately calculating laminar flame velocity, flame surface thickness and their variations with pressure was proposed. The large eddy simulation, chemical reaction model and multi-component reaction flow finite difference simulation code were integrated to carry out the numerical simulation of hydrogen air explosion in closed pipes. The effects of large eddy simulation model, grid size and chemical reaction model on the calculation results and efficiency were studied by comparison with experiments. The results show that compared with the detailed reaction model, the new single step hydrogen air simplified reaction model saves 60% of calculation time, and greatly improves the calculation efficiency of three-dimensional numerical simulation of gas explosion.