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Polymer electrolytes have great potential to realize solid‐state lithium metal batteries with high energy density and intrinsic safety. However, the poor mechanical strength and uncontrolled electrolyte/electrode interface cannot guarantee the stable operation during long‐term cycling. Herein, a supramolecular polyurethane material reinforced by aromatic charge‐transfer interactions is synthesized as electrolyte matrix with high stiffness, excellent toughness, and unique mechanical energy dissipation capacity. The optimized electrolyte network can dynamically adapt to the volume fluctuating Li metal and, importantly, eliminate stress‐concentrating behavior under deformed state. As a result, the Li/Li symmetric cells can stably work for more than 3500 h without short circuit. And the LiFePO4/Li batteries show superior electrochemical performance over 1200 cycles with a capacity retention of 95.4% at 0.33 C. The supramolecular approach to tune the mechanical properties of the polymers is believed to provide a new strategy for designing solid electrolytes with desirable comprehensive mechanical properties for solid‐state batteries. [ABSTRACT FROM AUTHOR]