Abstract: At present, poor interfacial stability at high voltage is a thorny problem hindering the development of high-performance all-solid-state batteries. Optimizing the cathode/electrolyte interphase (CEI) is currently the mainstream method, and a uniform and stable CEI can significantly improve the cycling performance of the battery. However, the composition of CEI is complex, the thickness and uniformity are difficult to control, and its ionic conductivity and stability are poor, which seriously hinder the development of lithium-ion batteries.Therefore, it is extremely important to optimize the performance and stability of CEI. In this paper, the composition and structure of CEI are first expounded, and then the formation mechanism and function of CEI are introduced, and then the modification strategies to improve the performance of CEI are systematically analyzed, such as the improvement of CEI by lithium salt optimization, additive regulation, artificial construction of CEI, etc., and finally, the challenges and future development trends of CEI in the research process are summarized.