The invention discloses a working method of a lithium battery assembling device. The working method comprises the following specific working steps that step 1, a second stepping motor drives a rotating shaft to rotate, the rotating shaft enables lithium batteries to be conveyed all the time through a conveying assembly, meanwhile, the rotating shaft sequentially transfers rows of lithium batteriesinto a fixing frame through a displacement mechanism to be arranged, and the fixing frame is pushed backwards for a certain distance each time; and step 2, the fixing frame is filled with the lithiumbattery, the fixing frame is pushed out of a spacing bar for the last time, an abutting block is not abutted against by the spacing bar any more, and an opening and closing plate is closed. The working method has the advantages that the structure is reliable, a square frame can continuously and automatically drive the lithium batteries to move backwards, ascend to be separated from the lithium batteries and move downwards to cover the lithium batteries after moving forwards, meanwhile, the conveying assembly can fill the lithium batteries until the fixing frame is fully with the rows of lithium batteries, meanwhile, the fixing frame is pushed backwards, automatic closing of the fixing frame is achieved, then a new fixing frame is conveyed and the finished fixing frame is moved away, the automation degree is high, and the working efficiency is improved.