Abstract: The basic theory of the ultrasonic guided wave detection technique was reviewed. Using the finite element method, numerical simulation studies were performed about the T(0,1) modules applied in the current detection in field. In finite element models, the defect and welding were simulated by getting rid of or add some cells at specific position, and the T(0,1) modules wave-input was simulated with tangent transient displacement applied at one end of pipe. The results showed that the corrosion defect was located by the time of the echo wave and the wave velocity. At the same time, the relationship between reflection coefficient and the geometrical dimension of defection was made. The flaw and the welded joint can be distinguished by the echo initialphase.