Abstract: An excitation frequency is one of the control parameters of the selective thermal excitation detection technology. The study was started from the perspective of structural resonances. A simply supported concrete beam having micro-cracks was chosen as an incentive target and its natural frequency as the excitation frequency, which tested the incentive effect. And a 40 kHz excitation frequency was chosen as an objective of the comparison tests. The experiment results show that the simply supported concrete beam excited by the 40 kHz frequency has a significant thermal excitation effect, but this effect is not excited by the natural frequency. Both macroscopic overall vibration and microscopic particles fluctuations in the simply supported beam influence the excitation effect. Based on the experimental phenomenon, the influences of two vibration conditions on the thermal excitation effect and the interaction between two vibrations were analyzed in the aspect of mechanism. Analysis results show that the thermal excitation ability of the overall vibration is weaker than that of the particles fluctuations during the whole process of excitation, and the overall vibration continues to weaken the strength of the particles fluctuations throughout the whole excitation process. The microscopic particles fluctuations can excite the thermal excitation effect. The 40 kHz ultrasonic frequency can be used to reduce the overall vibration strength, so as to eliminate the attenuation of the overall vibration to the particles fluctuations.