Abstract: In order to improve the safety of lithium ion batteries and reduce safety accidents caused by thermal runaway of lithium ion batteries, this paper uses a commercial 18650 ternary lithium ion battery as the research object, and establishes a three-dimensional thermal runaway model induced by high temperature through COMSOL Multiphysics 5.6. By comparing temperature rise curves under different induced temperatures and different heat transfer conditions, the influence of induction temperature and heat transfer coefficient on the thermal runaway of lithium ion batteries is analyzed and explored. The results show that under different temperatures, the higher the induced temperature is, the higher the thermal runaway temperature peak is and the earlier the thermal runaway occurs. Under different heat transfer conditions, the larger the convective heat transfer coefficient is, the earlier the thermal runaway occurs and the larger the temperature drop gradient is after reaching the peak. Besides, the participation of cathode materials in the reaction can be regarded as a key characteristic of thermal runaway.