The stability of solid electrolyte interphase (SEI) is one of the most critical factors that determines the performance of alkali metal anodes. Although extensive and advanced methods have been carried out to study SEI of Na metal anodes, the structural/componential evolution is still uncharted territory due to its transient formation and complicated components. Herein, the SEI formation and dissolution processes are investigated by combining multiple in situ characterizations. By revealing spatial-temporal-resolved information about SEI evolution, an important failure mechanism is unveiled: a poorly passivated surface during the initial stage subsequently leads to a homogeneous distribution of organic and inorganic species, which is associated with structural instability. The developed methodology, combining multiple in situ characterizations, can be further employed to study interfacial evolution in other systems of batteries, providing guiding significance in unveiling interfacial chemistry.