The invention relates to the preparation method of a lithium iron phosphate power polymer lithium ion battery. The method mainly comprises following steps: preparing electrode slurry, processing a current collector, preparing a positive electrode sheet, preparing a negative electrode sheet, preparing a membrane and preparing a single battery sheet. By adopting lithium iron phosphate as the positive electrode material and stacking process, the invention can significantly improve the safety performance, cycle performance, etc. of the battery to well meet the performance requirement of power supply.