The safety issue of lithium ion battery is still a big challenge especially at high temperature. To solve the problem, the biodegradable copolymer P(LA-co-TMC) (Poly Lactide-Trimethylene Carbonate), as a brand new polymer electrolyte host, is firstly applied in lithium ionic battery. A novel composite solid polymer electrolyte (CSPE) was prepared by dip-coating P(LA-co-TMC)/succinonitrile/LiTFSI (P(LA-co-TMC)-SPE) into Celgard 2325 membrane. The results of IR, XRD and SEM demonstrated that the Celgard 2325 membrane was completely coated and permeated by P(LA-co-TMC)-SPE. And the DSC results revealed that the thermostability of CSPE was improved. This CSPE showed high ionic conductance, high lithium ion transference number t(Li)(+) = 0.563) and wide electrochemical window ( > 5.2 V). The all-solid-state lithium ion battery with the CSPE based on P(LA-co-TMC) exhibited outstanding cycling performance and > 98% coulombic efficiency at 55 degrees C. Furthermore, it also presented high capacity retention (nearly 100% when returning to 0.1 C) and attractive capacities of 130.4, 122.3, 93.6 and 46 mAh g(-1) at C-rates of 0.1, 0.2, 0.5 and 1 C, respectively. From all the results above, the novel CSPE, with high electrochemical performance and safety at elevated temperature, is a good candidate for the application of all-solid-state lithium battery.