Abstract: Lithium-ion battery (LIB) develops rapidly due to its high energy density, easy maintenance, long cycle life, and low environmental pollution. Nowadays, LIB has become the first choice for electric vehicle power systems. However, the lithium-ion battery shows a poor thermal stability, it may be fired at some abused conditions resulted in explosion accident and even personal injury. The safety issues of lithium-ion battery hinder the development of other relevant fields such as electric vehicles seriously, therefore, in-depth research on battery safety is imperative. The recent accidents about electric vehicle caused by lithium-ion battery firing and the research progresses about LIB safety were summarized in this paper, and the chemical reaction mechanism of lithium-ion battery during thermal runaway was discussed in detail based on the research on thermal safety of LIB over the world. It is found from the resent research that the spontaneous firing of LIBs is one of the main causes of frequent accidents in electric vehicles. Although the great progresses have been made in current researches on the thermal runaway reaction mechanism and influencing factors of LIBs, there are still few studies about the detailed mechanism and propagation process of battery flame, and no effective solution for battery firing issues has been found. Thus, how to improve battery safety performance is still an urgent problem to be solved.