As the main power source for electric vehicles, lithium-ion power batteries have always been the focus of public safety. Lithium-ion batteries may occur thermal runaway after internal short circuit caused by mechanical abuse. It is extremely important to study the influencing factors of thermal runaway. In this article, the quasi-static battery extrusion test is used to study the changes of load, voltage, and temperature during the short circuit process of lithium-ion batteries and to observe the influencing factors that may cause thermal runaway. The electrochemical–electrical–thermal multi-physics coupling model was established by comsol multi-physics simulation software to simulate the thermal behavior of the battery after short circuit. The effects of short circuit cases, state of charge (SOC), and voltage maintenance time after short circuit on the thermal runaway of the battery are studied. By comparing the experimental results, the short circuit case of the battery caused by mechanical abuse is judged. The research results have played a certain reference role in the future research on battery mechanical abuse and internal short circuit.