In order to improve the low thermal conductivity of phase change materials for battery thermal management, paraffin-expanded graphite composite phase change materials with various contents were prepared. In the phase change energy storage unit, PA-EG composite phase change materials are used to wrap the heat source and the heat pipe is coupled to enhance its heat dissipation capacity. A square heating source is used to simulate the heating of a high-density energy battery, and the thermal management performance of the PA-EG composite phase change materials coupled heat pipe with different EG content is explored under different heating powers. The experimental results show that when the heating power is low, the thermal management performance of each phase change material is equivalent. When the heating power is higher, the higher EG content will bring higher thermal conductivity and better thermal management effect. When the EG content is 5%, the thermal conductivity can be increased to 6.36 times that of paraffin. The maximum cooling rate in the experiment can reach 7.6%, and the peak temperature difference in the phase change energy storage unit is 37.7% of that in the paraffin system. When the content of EG is low, the thermal conductivity of PA-EG composite phase change material is isotropic when it is not melted, but when the PA is melted, the strong natural convection heat exchange will cause uneven temperature distribution in the energy storage unit. It will easily lead to uneven temperature on the battery surface to produce stress, so the EG content should not be less than 5%.