The thermal failure propagation is one of the most severe challenges for battery pack and it usually aggravates the thermal hazards, further resulting in serious accidents. A series of thermal failure researches were conducted to explore the effects of state of charge (SOC), the number of heaters, failure location and pack size on the thermal failure propagation of battery pack. According to the results, it is found that there exists an obvious domino effect in the thermal failure propagation of battery pack. Typically, the thermal failure of battery pack can be divided into several phases. The higher SOC worsens the propagation of battery pack. Besides, the thermal failure appears earlier for the pack with larger number of heaters. If the battery close to the center of pack takes thermal failure, the failure propagation will be aggravated. Moreover, it is exhibited that the thermal failure propagation will be delayed longer when failure propagates to the outermost layer of batteries with the increase of pack size. (C) 2018 The Electrochemical Society.