Metal-return line arresters play a crucial role in high-voltage direct current (HVDC) power transmission systems by absorbing excess energy on the metal-return line. However, comprehensive research on the operational characteristics of metal-return line arresters in Extra-high-voltage direct current (EHVDC) systems remains limited. This paper establishes a model of the ±660 kV EHVDC transmission system and studies the energy absorption of metal-return line arresters under different operating conditions. It not only presents the voltage and current waveforms and energy absorption of the metal-return line arresters when an overvoltage occurs on the busbar but also reveals the influence of different fault conditions and relay protections on the energy absorption of the metal-return line arresters. This analysis helps provides a reference for the protection design in EHVDC systems, thereby improving the overall system’s safety.