An efficient battery thermal management system (BTMS) will undoubtedlypromote the performance and lifespan of battery packs. In this study, a novelflame-retarded composite PCMs composed by paraffin (PA), expanded graphite (EG), ammonium polyphosphate (APP), red phosphorus (RP) and epoxy resin (ER) has been proposed for battery module. The thermophysical and flame retardant properties are investigated at both macro and micro levels. The results show that the proposed composite PCMs with an APP/RP ratio of 23/10 exhibit the optimum flame retardant performance. Besides, the APP/RP-based composite PCMs for 18650 ternary battery module has also been researched comparing with air cooled and PCM with pure PA modes. The experimental results indicated that the fire retardant PCMs shown significant cooling and temperature balancing advantages for battery module, leading to a 44.7% and 30.1% reduction rate of the peak temperature and the maintenance of the maximum temperature difference within 1.36°C at a 3 C discharge rate for 25°C. Even at 45°C, the temperature uniformity can still be controlled within 5°C. Thus, this research indicates the composite PCM had good flame retardant and form stable properties, it would be utilized in BTMS, energy storage and other fields.