A method for activation of a lithium secondary battery according to the present invention comprises a pressurization process for pressurizing the lithium secondary battery while changing pressure before an activation process, after the activation process, and in one or more selected from intervals between the activation steps. Accordingly, a bubble in an electrolyte or gas generated in an activation process is moved to a gas pocket part to prevent inner gas from being captured in an electrode assembly, thereby improving a performance of the battery.