Abstract: To study the law of oil & gas explosion overpressure and flame propagation of slender pipelines with large lengthto-diameter ratios in confined space in oil storage and transportation engineering, an oil and gas explosion experimental system for slender pipelines with different length-to-diameter ratios was set up. By acquiring and analyzing the explosion overpressure value, flame propagation speed, flame intensity and other parameters, the results show that the long-distance pipeline exerts significant reinforcement on explosion overpressure and flame propagation, which may induce the detonation when the length-to-diameter ratio exceeds a certain value. The detonation time of open pipeline comes earlier than that of closed pipeline. The flame propagation speed increases sharply from the middle of the pipeline, and the increase rate in open pipeline is larger than that of closed pipeline. The flame intensity goes up, from the middle to the end, in the closed pipeline, but goes down in the open pipeline. The experimental data could provide references for the safety of oil storage and transportation and protective design.