The present invention relates to a novel process for preparing a lithium polymer secondary battery which comprises a step of direct coating of a plasticized and crosslinked polymer electrolyte onto a lithium electrode. The process for preparing a lithium polymer secondary battery comprises the steps of: (i) dissolving a mixture of a crosslinking agent and a monomer in a molar ratio of 1:1 to 1:11 in a liquid electrolyte of 100 to 400% (w/w) to obtain a polymer electrolyte; (ii) applying the polymer electrolyte onto one side of a lithium electrode and treating with heat or UV to obtain a polymer-coated electrode; and, (iii) bonding the polymer-coated electrode to a positive electrode. In accordance with the present invention, a lithium polymer secondary battery with an improved interfacial stability between a lithium electrode and a polymer electrolyte can be prepared in a simple manner, which makes possible its wide application in the development of lithium polymer secondary battery.