Digital signal processor (DSP) is used to obtain the peak value and the time difference of ultrasonic signals, to make digital filter, and to derive mathematical transformation from analog circuit. In this study, C-scan system and control program have been developed to high speed data acquisition. This system consists of signal processing parts (DSP, oscilloscope, pulser/receiver, digitizer), scanner, and control program. The developed system has been applied to a practical ultrasonic testing in overlay weld, and demonstrated high speed with precision