Abstract: The basic theory of ultrasonic guided wave testing is introduced. By using different number of piezoelectric transducers, and adopting 10 cycles of modulated sinusoidal signal at 70 kHz through Hanning window, ultrasonic guided wave testing experiments in small-sized stainless pipe(8 mm in diameter and 1.5 mm in thickness) with crack defect and no defect are respectively conducted. The frequency dispersion and multi-mode phenomenon of guided waves is discussed. L(0,1) mode is excited successfully, and the results show that for such a small pipe, the echo waveforms are better by using two transducers to excite and other two transducers to receive. In addition, a certain size crack defects can be detected effectively.