Thermal runaway (TR) and its propagation behavior in the large format lithium-ion battery (LIB) with various states of charge (SOC) are experimentally investigated in this work. Thermal runaway feature of the cell under thermal abuse condition is characterized using extended volume accelerating rate calorimeter. Based on the experimental results, the modules with five LIBs are built to analyze TR propagation mechanism and further discuss the impact of SOC on TR propagation behavior. It is found that the TR is firstly triggered on the layer near the front surface of the LIB, and then spread to the whole battery. The average propagation time inside the single LIB is 10 s in the module with 100% SOC while 39 s in the module with 50% SOC. Moreover, the module with 100% SOC shows intense combustion behavior, which is replaced by a considerable amount of smoke in the module with 50% SOC. Besides, the average propagation time between adjacent LIBs is significantly delayed from 87 s in 100% SOC module to 307 s in 50% SOC module. This work details lit propagation feature in large format LIB pack, and can provide the guidelines for the safety design of lithium-ion battery module.