The utility model discloses a lithium ion battery fixing device. The lithium ion battery fixing device comprises a rectangular box body and an adapter plate arranged inside the box body, wherein a signal interface and a plurality of metal bonding pads for sequentially connecting lithium ion batteries in series are arranged on the upper surface of the adapter plate; at least a pole ear fixing hole is formed in each metal ponding pad; the signal interface is electrically connected with all metal welding pads through printed conducting wires; a plurality of arranged vent holes are formed in an upper box board of the box body; at least one cooling exhaust fan is arranged on a lower box board of the box body; the area of the adapter plate is smaller than that of the upper box board; two extension plates are arranged on the upper box board or the lower box board. The lithium ion battery fixing device disclosed by the utility model has the characteristics that the assembled battery pack is high in stability, safety, reliability and quality consistency.