In order to study the electric thermal behavior of lithium iron phosphate power batteries at different ambient temperatures, the 100% SOC 23 Ah lithium iron phosphate batteries were overcharged at ambient temperatures of-25, 0, 25, 50 and 75 ℃at 1C rates until the battery spray valve occurred. It is found that the exhaust volume and exhaust time when overcharging to the spray valve increase with the decrease of ambient temperature. According to the change trend of voltage in the overcharging process, it can be divided into 5 stages at low temperature, 4 stages at room temperature, and 3 stages at high temperature, and the voltage change stage decreases with the increase of ambient temperature. When overcharging at extremely high temperatures, it is easy to trigger thermal runaway. The low temperature environment can effectively suppress and alleviate battery failure and thermal runaway; When over-charged, the internal resistances of the battery are increased, and the PTC protection device is triggered. If overcharging continues after triggering, the internal resistance of the battery decreases. This study will provide practical support for the early warning method to prevent thermal runaway induced by overcharging of power battery.