AbstractAll‐solid‐state lithium–sulfur batteries (ASSLSBs) are expected to be the next generation of high‐energy battery systems due to their long lifespan and high safety. However, unstable interfaces between elemental sulfur, conductive carbon, and solid electrolytes lead to slow charge transport and mechanical failures, thereby limiting battery performance. Herein, atomic layer deposition‐derived lithium phosphorus oxide is applied to the surface of carbon/sulfur particles to enhance the interfacial stability of the sulfur cathode and improve the electrochemical performance of ASSLSBs. The coating layer can inhibit electrolyte decomposition and improve interfacial stability by blocking electron conduction between carbon and electrolyte. Moreover, it not only serves as an ion‐conducting layer to facilitate Li⁺ transport but also acts as a stress buffer layer to alleviate contact failure. The assembled ASSLSBs with sulfide electrolyte exhibit an initial specific capacity of 1322 mAh g⁻¹ at 0.2 C and capacity retention of 86.4% after 300 cycles. Furthermore, ASSLSBs maintain a reversible capacity of 645 mAh g⁻¹ at 0.5 A g⁻¹ after 1000 cycles, confirming the long cycling stability of the coated sulfur cathode. Even under high sulfur loading, ASSLSBs achieve high areal capacities of 4.6 mAh cm⁻² at 30 °C and 11.7 mAh cm⁻² at 60 °C.