Abstract: In order to analyze the effect of different exciting modes on ultrasonic testing signal, the characters of ultrasonic testing signals received from carbon fiber reinforced plastics(CFRP) and aluminum alloy which were tested by ultrasonic transducer were analyzed, and the transducer was simulated by sharp pulse and square pulse. The experimental results proved that the amplitude of ultrasonic testing signal excited by square pulse was 2 times of that excited by sharp pulse on the same voltage, and the noise in echo signal which was generated by square pulse was stronger than sharp pulse. The square pulse is therefore fitter to test CFRP than sharp pulse during the producing and operating process.