Stable solid electrolyte interface (SEI) is the key to improve the electrochemical performance of lithium metal batteries. However, there are still many puzzles about SEI film that have not been well explained, due to the complexity of electrochemical reactions involving in SEI formation and the absence of direct observation methods for SEI. Here we realize the direct observation of SEI by skillfully designed fluorescent tracers acting as an SEI film‐forming additive for electrolytes. These fluorescent tracers have three important moieties: an olefin group for polymerization on anode surface so as to participate in SEI film formation during charge/discharge cycles, a polar group for Li‐ion conduction, and an AIEgen for fluorescent tracing. Therefore, the tracers participate in SEI film‐forming and result in a shining SEI film. This shining SEI film with intrinsic fluorescence signal allows direct observation and quantification on the distribution, relative abundance, and macro morphology of SEI. These fluorescent tracers can also reveal the SEI formation‐growth‐destruction regularity during charge/discharge cycles. Several summarized typical macro morphologies and evolution stages of SEI would enrich our knowledge and understanding of SEI, and help us to gain insight into the interaction between electrolyte and anode, electrochemical performance and cycle life of batteries.This article is protected by copyright. All rights reserved