Abstract: Boiling over of oil storage tank is one of the problems encountered in fighting tank fires? This article an a lyses the main conditions which can result in boiling over: ① crude oil shows a moving thermal wave characteristic; ② crude oil contains water; ③ crude is more or less viscous and can form oil foam; and ④ there is not enough space over the liquid level for expansion. Introduced in this paper are the characterization parameters of oil thermal wave characteristics, including propagation speed, temperature of the stable high temperature layer, and burning speed. Also stated based on the experimental data is the relationship between these parameters and the oil composition, tank diameter and water content. According to the characteristics and risks of boiling over, such suggestions are given as properly determining the times of distinguishing and boiling over, and preventing water from flowing into tank.