With the coming era of large-scale energy storage, development of next-generation non–Li-based rechargeable battery technologies is imperative. Owing to the abundance, economy, and high energy density, K-ion batteries (KIBs) have attracted much attention. However, the overlarge K-ion can greatly destroy the electrode materials during potassiation-depotassiation process, resulting in a sharp decrease of the cycle life, which will enormously restrict the applications of KIBs. Currently, one of the effective strategies is adopting potassium bis(fluorosulfonyl)imide (KFSI) to replace conventional KPF as solute in electrolytes. Such KFSI-containing electrolyte can induce forming stable solid-electrolyte interphase (SEI) layer, which is in favor of the stability of electrode material after cycles. In this review, we summarize all current materials cooperated with KFSI-containing electrolytes for KIBs and attempt to provide a better understanding of the improving mechanism for K-ion storage and the effect of the unique SEI layer. In addition, some critical issues and perspectives of KFSI-containing electrolytes for K-ion storage are also discussed, which will provide a developmental direction of KIBs.