This paper simulate the effect of high temperature on thermal safety on ternary soft-packed lithium-ion battery by heat treatment lithium-ion battery at 80℃. Compared and analyzed thermal runaway temperature, voltage and dV/dQ curve of battery. It is found that with the increase of heat treatment times, the charge and discharge capacity of the battery decreases in turn, and the third time heat treatment has the most significant effect on the battery capacity. The damage degree of the internal structure of the battery increases gradually, the internal structure of the battery becomes fragile in turn, and the time of thermal runaway is getting earlier. The harmfulness of thermal runaway decreases gradually, the maximum temperature of battery thermal runaway decreases in turn.