| In this paper, the parallel ventilation structure of battery box for hybrid electric vehicle is improved by optimizing the original parallel ventilation structure. Uniform cooling between the front surface and the rear surface of battery can be ensured. According to the air inlet mode and flow path structure, three kinds of structures, i.e., wedge shaped structure, trapezoid structure and circular hole baffle structure, are designed. It is shown that the circular hole baffle structure is the best. Meanwhile, the structure of the circular hole baffle is improved in cooling dimension. Parallel cooling and vertical cooling are demonstrated. The results show that the dual channel vertical cooling structure is the better. In the condition of ambient temperature less than 30 ℃, cooling effect is the best at medium and low discharge status when the outlet flow velocity is 6 m?s-1 and the battery gap is 4 ~ 6 mm.