Abstract To improve the thermal management performance of Li-ion power battery packs, this paper investigates HP/PCM (heat pipe/phase change material) coupled thermal management (TM). The significant purposes are to reveal internal coupled heat transfer mechanism, and propose a critical application range of coupled TM. To achieve this goal, lumped parameter method and finite difference method are adopted to build the mathematical modelling. Based on the simulation, the superiority of temperature control in coupled TM can be confirmed, and its internal heat flux distribution is calculated to reveal the principle of temperature control effects. Further parametric study is carried out to analyze their variation trend over different working conditions, whereupon both coupled heat transfer mechanism and critical application range are obtained. Results demonstrate that coupled TM achieves lower battery surface temperature and longer control time compared with single HP and PCM TM, respectively. It also shows that internal coupled heat flux distribution transits from PCM-dominated to HP-dominated, and ultimately almost depends on HP. Furthermore, based on the data of parametric study, coupled TM plays superiority when h