All‐solid‐state polymer electrolytes (ASPEs) with excellent processivity are considered one of the most forward‐looking materials for large‐scale industrialization. However, the contradiction between improving the mechanical strength and accelerating the ionic migration of ASPEs has always been difficult to reconcile. Herein, a rational concept is raised of high‐entropy microdomain interlocking ASPEs (HEMI‐ASPEs), inspired by entropic elasticity well‐known in polymer and biochemical sciences, by introducing newly designed multifunctional ABC miktoarm star terpolymers into polyethylene oxide for the first time. The tailor‐made HEMI‐ASPEs possess multifunctional polymer chains, which induce themselves to assemble into micro‐ and nanoscale dynamic interlocking networks with high topological structure entropy. HEMI‐ASPEs achieve excellent toughness, considerable ionic conductivity, an appreciable lithium transference number (0.63), and desirable thermal stability (Td > 400 °C) for all‐solid‐state lithium metal batteries. The Li|HEMI‐ASPE‐Li|Li symmetrical cell shows a stable Li plating/stripping performance over 4000 h, and a LiFePO4|HEMI‐ASPE‐Li|Li full cell exhibits a high capacity retention (≈96%) after 300 cycles. This work contributes an innovative design concept introducing high‐entropy supramolecular dynamic networks for ASPEs. A rational concept of high‐entropy microdomain interlocking all‐solid‐state polymer electrolytes is designed by introducing newly polymerized multifunctional ABC miktoarm star terpolymers into polyethylene oxide. The tailor‐made electrolyte shows advanced mechanical, electrochemical, and thermodynamic performances, stably enabling all‐solid‐state Li metal symmetrical cell cycles over 4000 h.