Objective To analyze the causes and suspicious risk factors of a flash explosion incident of a Yangtze River shipping cargo ship,and provide a reference for laboratory detection of similar incidents. Methods According to the existing detection methods in the laboratory,triple four pole GC-MS was used for the qualitative analysis of unknown substances.GC-MS and gas chromatography were used for the quantitative comparison of unknown substances at the same time to ensure the accuracy and reliability of quantitative results and find the cause of cargo ship flash explosion. Results The on-site air was collected from the cargo ship after the flash explosion:the contents of n-hexane and ethyl acetate were determined in 3 air collecting bags and 20 activated carbon rod adsorption samples.No volatile toxins were detected in the three bag samples.The maximum content of n-hexane in the activated carbon rod adsorption samples was 33 310 mg/m³,and the maximum content of ethyl acetate was 38.3 mg/m³. Conclusion The flash explosion of the cargo ship is caused by n-hexane.The triple four pole GC-MS was used for qualitative judgment of unknown substances,and the GC-MS and gas chromatograph were used for comparison and quantification of unknown substances at the same time,so as to quickly find out the cause of flash explosion of the Yangtze River shipping cargo ship.