The performance of the hydrogen power system is a critical factor in the design of fuel cell electric vehicles, as it includes the device's characteristics, control effectiveness, and energy management outcomes. This study investigated a typical hydrogen power system that uses a metal hydride (MH) hydrogen storage tank and a proton exchange membrane (PEM) fuel cell. The aim was to evaluate the thermal coupling effects of the MHPEM hydrogen power system through mathematical modeling and realworld traffic testing. First, a multiphysical field coupling model of the MHPEM hydrogen power system was proposed based on the structure of the thermal exchange system. Then, numerical simulations and experiments were conducted based on the operating conditions of a rangeextended fuel cell hybrid electric vehicle. The results indicated that the proposed mathematical model can accurately characterize the dynamic features of the onboard hydrogen energy system. The comparison of simulation and experimental results showed great agreement, particularly in terms of power response and temperature dynamics. Further analysis of the influence of atmospheric temperature on the hydrogen supply flow was carried out by examining the temperature variation in the MH tank. The results show that the thermal coupling design is an effective method for improving energy efficiency. The results of this study may be used for optimal sizing, temperature control, and energy management strategy design of MHPEM hydrogen power systems.