<p>Compared to determining cable ampacity based solely on the maximum ambient temperature, analyzing the heat transfer characteristics of buried cable groups taking into account the real-time ambient temperatures that vary with diurnal cycles and seasons enables more accurate calculation of conductor temperatures, thereby fully exploiting the current-carrying capacity of power cables in depth. This paper first established a finite element calculation model for the temperature field of directly buried cables under constant ambient temperature. The simulation results reveal a time delay between cable heating and the corresponding temperature change at the ground surface, demonstrating the thermal inertia inherent in heat transfer for buried cables. Subsequently, a coupled electromagnetic-thermal finite element model for groups of directly buried cables is developed, incorporating long-term, real-time ambient temperature boundary conditions at the ground surface. Long-term conductor temperature calculations under step-load conditions are performed. Compared with the constant ambient temperature scenario, the conductor temperature under real-time surface ambient conditions varies dynamically with ambient temperature and remains significantly lower, confirming substantial available a large current-carrying capacity expansion space for buried cable groups. Finally, the influences of burial depth and the number of cable circuits on conductor temperature and ampacity under real-time ambient temperature are analyzed, providing a basis for dynamic load-based ampacity enhancement of buried cable groups.</p>