The invention provides a method for manufacturing a lithium ion battery by using a gel diaphragm. The method comprises the following steps of manufacturing a positive pole piece, manufacturing a negative pole piece, baking the pole pieces, laminating, preheating, carrying out primary hot pressing, carrying out primary cold pressing, manufacturing a battery cell, pre-charging, ageing, carrying outsecondary hot pressing, carrying out secondary cold pressing, forming and finishing the manufacturing of the battery cell. According to the manufacturing method of the lithium ion battery using the gel diaphragm, the gel diaphragm is adopted, firstly, preheating, hot pressing and cold pressing are conducted on the core package after lamination, and in the stage, the pressure of hot pressing and cold pressing is small, so that the gel diaphragm slightly adheres to a pole piece to achieve a fixed core package structure. Secondly, pressure is applied to the battery cell in a pre-charging stage; and finally, the procedures of hot pressing and cold pressing are added before the formation procedure, so that the tight bonding of the positive/negative pole piece and the gel diaphragm is realized.