Abstract: The excitation efficiency and mode selection of ultrasonic Lamb wave mixing were studied. Based on the non-zero energy flow and matching conditions, combined with the distribution of Lamb wave in the structure, the excitation efficiency parameter was proposed as the basis for ultrasonic Lamb wave mixing mode selection. Based on the wave mixing conditions, the mode pairs were selected and excitation efficiency parameters were calculated. The effectiveness of the excitation efficiency parameter was verified through simulation and experimental measurements of ultrasonic Lamb wave mixing. Comparing the relationship between nonlinear parameters and excitation efficiency parameters obtained from simulation and experiments, the effectiveness of excitation efficiency parameters as a basis for mode selection has been demonstrated. Therefore, the excitation efficiency parameter can effectively characterize the excitation efficiency of ultrasonic Lamb wave mixing, thereby achieving the screening of mode pairs with obvious nonlinear effects for better detection and characterization of damage.