The invention provides a fireproof device of a lithium ion battery. A fire-resisting passageway is formed by a fire-resisting space inlet, multiple first openings, multiple second openings and a fire-resisting space outlet. The space in a fire-resisting space is fully utilized by the fire-resisting passageway, and flames generated by eruptive materials flow through a long path in the fire-resisting space. When the flames generated by the eruptive materials flow in the fire-resisting passageway, heat losses of the flames generated by the eruptive materials can be increased suddenly, and the flames generated by the eruptive materials are obstructed, so that burning cannot continue, and the flames are extinguished. The flames generated by the eruptive materials can hit against second fire-resisting plates, first fire-resisting plates, an inlet baffle and an outlet baffle, a chain reaction is stopped through the wall effect, wall face heat transfer is facilitated, the destroy rate of active groups can be increased, and therefore fire catching cannot continue.