Efficient heat transfer is still one of the major concerns to be solved in battery thermal management technology. This paper proposes a battery thermal management method based on silicon oil. With this method, the battery pack is totally immersed in silicon oil, through which the generated heat during dis/charging is dissipated. To evaluate the performance of this proposed thermal management method, the electrochemical-thermal coupling model of a lithium battery pack with 12 50Ah cells in series is established, based on which the electrical and thermal performance of the pack is simulated. The results show when discharging at 1C rate, the overall temperature of the battery pack immersed in the silicon oil is 0.5 °C lower than that of the traditional air cooling. In addition, through experiments, this paper verifies that the proposed thermal management method based on silicone oil has no negative impact on the normal operation of the battery. Moreover, silicon oil can prevent the occurrence of thermal runaway to a certain extent, improving the safety of lithium battery.