The intrinsic instability of organic electrolytes seriously impedes practical applications of high‐capacity metal (Li, Na) anodes. Ion–solvent complexes can even promote the decomposition of electrolytes on metal anodes. Herein, first‐principles calculations were performed to investigate the origin of the reduced reductive stability of ion–solvent complexes. Both ester and ether electrolyte solvents are selected to interact with Li+, Na+, K+, Mg2+, and Ca2+. The LUMO energy levels of ion–ester complexes exhibit a linear relationship with the binding energy, regulated by the ratio of carbon atomic orbital in the LUMO, while LUMOs of ion–ether complexes are composed by the metal atomic orbitals. This work shows why ion–solvent complexes can reduce the reductive stability of electrolytes, reveals different mechanisms for ester and ether electrolytes, and provides a theoretical understanding of the electrolyte–anode interfacial reactions and guidance to electrolyte and metal anode design. The origin of reduced stability: The reason why ion–solvent complexes promote electrolyte decomposition on alkali/alkaline earth metal anodes is probed. The complexed cations can regulate the contribution ratio of carbon atomic orbitals in LUMOs of ion–ester complexes or totally change the atomic contribution in LUMOs of ion–ether complexes to reduce the energy level of the LUMO.