The invention relates to a method and a device for restraining and preventing thermal runaway of a lithium ion battery. According to the method, a liquid inert gas is utilized to perform spraying refrigeration and fire fighting on a faulted lithium ion battery. The method comprises the following steps: A, selecting spraying time; B, determining the spraying quantity of a sprayed gas; C, determining a spraying mode, wherein the spraying mode refers to continuous spraying or interrupted spraying. The device comprises a control cabinet, a storage tank, a main control valve, a secondary control valve, a nozzle, a detector and a safety valve, wherein the control cabinet is a manual button control cabinet or an automatic control cabinet provided with a PLC (Programmable Logic Controller); the detector comprises a temperature sensor used for monitoring the temperature of one or more battery monomers. The method and the device have the advantages that dual effects of refrigeration and fire fighting are achieved, a security mode is complete in functions, stable, safe, reliable and efficient, a vaporization product of the liquid inert gas is nontoxic, environmentally friendly and clean as well as free from secondary damages on battery equipment.