To research the thermal security of lithium-ion power battery used in electric vehicles, a kind of Lithium-ion power battery with 11 Ah rated capacity was taken as an example, and use the FEM software to conduct the finite element modeling and analysis. The effects of different discharge rates, different ambient temperature and different cooling conditions on the thermal characteristics of lithium-ion power battery were investigated. The simulation results illustrated that the higher discharge rate leads to the more and uneven temperature distribution; better cooling modes help to suppress the temperature rise and improve the thermal stability of the battery. The quantitative calculation and simulation results match well the actual conditions. The research results provide the reference for the modeling and simulation of this kind of batteries, which showed the guiding significance for design, optimization and battery thermal management system of lithium-on power battery monomers.