Abstract: Fire resources and leak of oil and gas result in fire and explosion in oil tank. The article applies the fault tree method to analyze the basic cause of the two major reasons. Based on the analysis result, the fault tree of oil tank is established. The minimal path sets (MPS) are achieved by Boolean algebraic simplification calculation. The authors put forward the analyzing result of the structural significance of the basic event. The basic factors resulting in fire and explosion in oil tank are investigated through the qualitative analysis. The authors bring up some relevant measures to prevent and improve the safety status in oil tank in the article.