Abstract: A method of ultrasonic C-scan imaging based on NC machine is presented in this paper. An experiment was conducted to analysis the motion characteristics of NC machines, then a model of its motion control was established in order to realize the synchronization of the ultrasonic signal acquisition and C-scan imaging. Then test-bed of automated ultrasonic testing was setup according to RS232. The results of ultrasonic C-scan experiments indicated the validity of the proposed system, which has the advantages of good versatility, easy to operate, low cost and high precision.