AbstractSolid‐state lithium metal batteries (SSLMBs) with polymer electrolytes (SPEs) have attracted tremendous attention owing to their superior safety and high energy density. However, the unstable solid electrolyte interphase (SEI) between Lithium (Li) and SPEs hinders their practical application. Herein, an innovative interfacial catalysis strategy is applied to the in situ construction of a multifunctional inorganic‐rich SEI. The transfer of unpaired electrons adjacent to calcium vacancies (VCa) to the TFSI− anion promotes the breaking of S─N and C─F bonds during the electrochemical decomposition of TFSI−, thus enhancing its decomposition kinetics. The inorganic‐rich SEI derived from TFSI− is super‐stable and kinetically favorable for fast and homogeneous transport of Li ions, thereby hindering the growth of lithium dendrites. Consequently, the interfacial catalysis strategy endows Li||Li symmetric cells, LFP||Li and NCM811||Li full batteries with enhanced cyclability. Thus, this work expands the interfacial catalysis strategy to a platform for designing multifunctional SEI in long‐life SSLMB.