The invention provides a lithium ion battery thermal runaway early warning method. The lithium ion battery thermal runaway early warning method comprises the following steps of: the step 1: performinganalog simulation on a lithium ion battery, obtaining shell surface temperature data and deformation data of the lithium ion battery at the normal charging and discharging moment and the overchargingthermal runaway moment of the lithium ion battery, and establishing a battery temperature distribution model; the step 2, in the battery temperature distribution model, determining the positions of asurface temperature highest point P1 and a surface temperature lowest point P2 when the lithium ion battery is normally used; the step 3, monitoring the temperature difference [delta]T and the deformation difference [delta]d between P1 and P2 of the lithium ion battery in the use process in real time by a monitoring device; and the step 4, determining the running state of the lithium ion batteryaccording to a preset condition. Through the combined use of the maximum temperature difference of the battery body and the shell deformation, the early monitoring of the battery thermal runaway can be effectively performed. Through condition logic determination, the possibility of thermal runaway of the battery is determined, and the accuracy is high.