A new method of coaxiality measurement of holes of large scale mechanical parts is studied.A single mode fiber (SMF) pigtailed laser diode alignment system provides a laser reference line with fine stability for measurement.The coaxiality can be computed from the measured coordinates of laser spot center and measured circumference data in several sections of holes.The results of measurement show that the method has good feasibility.The measuring system can be used for coaxiality measurement of large scale holes with high accuracy and flexibility.