With the electric vehicles used lithium manganese lithium-ion power battery (LiMn2O4 power battery) as the research object, the paper researched on the parameter identification of battery cell, has built the finite element model of single cell and completed the experimental verification. Also the paper has built the finite element model of both the battery box and battery pack, and analyzed the characteristics of temperature field distribution under two kinds of conditions, natural ventilation and forced ventilation.