Objective: To analyze the correlated risk factors of endodontic interappointment emergencies(EIAE) and the intervention effect of microwave endodontic sterilization. Methods: 163 patients with chronic periodontitis, pulpitis or dental pulp necrosis (without acute inflammation) were involved in the study. All the patients were distributed into microwave group (n=80) and control group (n=83) randomly. Unitarily finished endodontic therapy was conduced in microwave group after the microwave endodontic sterilization. Same endodontic therapy was applied in control group but without microwave endodontic sterilization. Risk factors of EIAE were investigated by releasing questionnaire. Logistic regression analysis was used to analyze the data. Results: Incidences of EIAE were related to age, gender, the position of the tooth, with or without fistula, filling condition and with or without microwave endodontic sterilization. The risk factors of EIAE of ultra-filling, posterior inferior tooth,the age older than 45 years and the female was 3.32,3.49, 5.87 and 3.71 respectively (P