Objective To evaluate the clinic effect of dental operating microscope ( DOM) and ul-trasonic root canal technique in removing fractured root canal instruments .Methods Eight cases with frac-tured instruments located in different parts of root canals were treated with ultrasonic technique under DOM and the results were analyzed .The fractured instruments were divided into stainless steel file , Ni-Ti file and post according to material type .Results Twenty-seven fractured instruments were removed and the total success rate was71.1%.Among them, the success rate of stainless steel file was 71.4%,of Ni-Ti file was 37.5%and of post was 100%.No root canal perforation occurred .According to the place fractured instru-ments located , the success rate of stainless steel file located at upper 1/3 root canals was 100%,at middle 1/3 was 81.8%and at apex 1/3 was 33.3%;the success rate of Ni-Ti file located at middle 1/3 was 60%and at apex 1/3 was 0.In bent root canals , the success rate of stainless steel file located at bent part crown square was 86.7%and at bent part apex square was 20%;the success rate of Ni-Ti file located at bent part crown square was 60%and at bent part apex square was 0.Conclusion DOM combined with ultrasonic root canal technique in removing fractured instruments is effective , but the success rate is relatively low for Ni-Ti files and the cases fractured instruments located at root canal apex 1/3 or bent part apex square .