Taking the “6·13” major gas explosion accident in Shiyan as the research object,this work constructed an accident investigation technique integrating scene investigation,interview and inquiry,numerical calculation and theoretical analysis.During the scene investigation,it was found that a section of DN57 mm medium pressure natural gas pipeline remained in the river below the southeast corner of the market.The pipe was adjacent to the domestic sewage drainage outlet,and it was rusted and partially ruptured due to the long-term wet environment.Meanwhile,yellowish natural gas fume was first found in the river at the southeast corner by video monitoring,visits and inquiries from surrounding residents,which led to the result that the aforementioned pipeline was the leak point.In addition,some merchants were engaged in flame operations before the accident.Some sparks entered the river through the smoke exhaust pipe and ignited the premixed combustible gas accumulated in the river,which resulted in the explosion.A numerical model of the river was established by the ANSYS/FLUENT software,and the volume of the natural gas accumulated in the riverway was 600 m3,which explosive TNT equivalent was 225 kg.The gas volume and explosion equivalent are consistent with the data published in the accident investigation,which proves the feasibility of this analysis method.