The invention discloses a polymer lithium ion battery and preparation method thereof. The method includes the following steps: a) preparing anode plate, lithium nickel, cobalt and manganate, conductive agent and bonding agent are dissolved into anode solvent to obtain anode size, and the anode size is coated on anode current collector; b) preparing cathode plate, graphite, conductive agent, bonding agent and tackify additive are dissolved into cathode solvent to obtain cathode size, and the cathode size is coated on cathode current collector; c) preparing DMC solution of PVDF, polyvinylidene fluoride (PVDF) is dissolved into dimethyl carbonate (DMC), so as to obtain DMC solution of PVDF; d) the anode plate and/or cathode plate are/is placed into PVDF solution; e) the anode plate and the cathode plate are baked and hot-pressed and then assembled with prepared diaphragm, and prepared lithium salt electrolyte is injected. The invention can obviously improve electrochemical performance ofbattery, improve cycling conservation rate of battery, ensures security performance of battery and reduces manufacturing cost of battery.