The mechanical damage evaluation of Z2CN18.12N welding joint with Lamb wave was concerned in this study. The excitation parameters were optimized from the aspects of number of cycles, central excitation frequency, and the electric fields excitation profiles of the piezoelectric transducers. Moreover, the influence of the mechanical clamping was also analyzed. Results show that the enhanced anti-symmetric wave mode under the anti-symmetric electric fields excitation was better regarded as the excitation signal and the optimum excitation parameters had a strong dependence on the mechanical clamping, which should be carefully considered. The corresponding waveforms under the optimum parameters could be clearly defined and separated with each other very well. This would provide a basis for the future study of online monitoring and evaluation.