In these years, the advantages of using phase change material in the thermal management of electric power battery has been wide spread. Because of the thermal conductivity of most phase change material (eg.wax) is low, many researchers choose to add high conductivity materials(such as black lead). However, the solid-liquid change material has large mass, poor flowability and corrosivity. Therefore, it still stays on experiential stage. In this paper, we use pure water as liquid phase change material (PCM), adopts PCM with an reflux device for thermal management. Meanwhile, utilizing the characteristics of pure water which are economical, easy to prepare, light weight, strong liquidity and hardly corrode the battery to explore the feasibility for water as a PCM for battery thermal management system. We use CATIA to build battery model and FloEFD to simulate temperature distribution of battery during its working stage. Furthermore, we also build a experimental bench and programming temperature control module to optimize the temperature control module, in order to develop a relatively perfect battery thermal management system. It is expected that the control precision of this temperature control module is less than 0.5 DEG C. Otherwise, the battery temperature could be kept around 30 DEG C and the maximum temperature is not more than 40 DEG C in this thermal management system.