Paraffin as a phase change material (PCM) is typically used in thermal management of Li-ion batteries. However, the low thermal conductivity of PCMs limits their use in high power devices. Superior thermal conductivity materials are often embedded in PCMs for heat dissipation in the passive thermal management system. In this work, copper fiber/paraffin composite phase change material (CPCM) was prepared based on solid-phase sintering technology. Li-ion batteries in four types of heat dissipation methods (natural wind cooling, filled with pure paraffin, copper foam/paraffin, and copper fiber/paraffin) were tested under different discharging currents. The effect of the porosity of copper fibers was also studied. The result indicates that copper fiber/paraffin CPCM can effectively improve the heat transfer performance and the uniformity of battery temperature within a 2 °C difference. Appropriately increasing the content of copper fiber is favorable to obtain high heat transfer properties of the material. It's predicted that porosity of 90% of copper fiber sintered skeleton offers the best performance of the composite material.