The finite element numerical simulation model considering the multi-physical field coupling between the ultrasonic and machinery in the piezoelectric material and the pipeline structure is established. The numerical simulation of the longitudinally guided wave excited by PZT actuator is carried out by using the ANSYS numerical analysis software to investigate the mechanism of the pipeline damage identification based on the piezoelectric ultrasonic. 16 PZT actuators are distributed circumferentially at the free end of each pipe model to excite the incident guided wave and a PZT sensor 50 mm apart from the actuator was used to receive the measured signals. The models of single crack pipes with different sizes are simulated numerically. The results show that the existence of defects in the pipeline can be identified accurately by using the longitudinally guided wave measurement method, and the echo amplitude is positively related to the size of the crack defect. At the same time, by analyzing the time history signal, the location of defects can be determined accurately.