The invention relates to the technical field of lithium ion batteries, and discloses a lithium ion battery steel shell and a method for improving the liquid injection efficiency of the steel shell. The lithium ion battery steel shell comprises a steel shell body, a fixing ring is fixed to the side wall of the upper portion in the steel shell body, a connecting cover is arranged on the lower portion of the fixing ring, the lower portion of the connecting cover extends to the lower portion in the steel shell body, and a plurality of ventilation openings are evenly formed in the outer wall of the connecting cover. The outer wall of the lower portion of the connecting cover is sleeved with a floating pad, a sealing ring is arranged on the outer wall of the through opening of the steel shell body, an exhaust mechanism is arranged in the sealing ring, one end of the exhaust mechanism is connected with the interior of the steel shell body, and the other end of the exhaust mechanism sequentially penetrates through the fixing ring, the sealing ring and the side wall of the steel shell body to be communicated with the outside. According to the invention, air can be exhausted in real time during liquid injection through the arranged exhaust mechanism, meanwhile, the arranged floating pad can move along with the liquid injection height, pressure of air on the upper portion is exhausted, and the air outlet efficiency is improved.