Root canal treatment is an important therapy for endodontic diseases. The efficiency and success rate of root canal treatment are on the rise with the development of multidisciplinary joint development, but there are still complications in the process of the treatment. Instruments separation is one of the most serious complications in the root canal treatment. As it occurs, it will seriously affect the efficacy and success rate of root canal treatment, which is a difficult problem for both patients and doctors. This article classifies instrument separation events while analyzes the reason of instrument separation and the factors affecting the occurrence of different types of instrument separation and the characteristics of each type of instrument separation from different perspectives. Through this article, clinicians can avoid the occurrence of instrument separation by analyzing the instrument separation events, and also have a proper analysis of the events that has occurred.