Complications of root canal treatment include: first, is an acute inflammatory reaction, after root canal filling, there will be a few patients with local swelling, itching and spontaneous pain. Generally, if there is no overfilling or underfilling on the radiograph, it is to take anti-inflammatory drugs for observation. If there is overfilling or underfilling, it is recommended to redo the root canal treatment; secondly, it is instrument separation, which is mainly due to improper operation of instruments during treatment, and the separation of instruments can also cause root canal perforation, root canal fracture, or even the worst ending is tooth extraction. The general treatment is to remove the fractured instruments or form a bypass under the microscope, and surgical treatment is also possible, and if necessary, the affected tooth is extracted; third, is pulpal perforation; fourth, is soft tissue chemical injury; fifth, is pulpitis; sixth, is root fracture. There are also other cases of resorption caused by periodontal tissues, accidental swallowing and swallowing of instruments, and some caused by the use of drugs.