A novel frequency domain assurance criterion, called hereby Spectral Assurance Criterion (SAC), is proposed for frequency response analysis of cracked piezoelectric beam under moving load. First, a model of cracked beam bonded with a piezoelectric layer under moving harmonic load is conducted based on the double beam conception and then, analytical expressions of midspan beam deflection (mechanical response) and output charge produced in the piezoelectric layer (electric response) has been established in the frequency domain. Crack-induced variations of the obtained frequency responses have been numerically examined by using the well-known coherence coefficient, like the Modal Assurence Criterion (MAC), between the frequency responses of intact and cracked beams. It is demonstrated that the mechanical and electrical responses are spectrally identical and robustly sensitive to crack and moving load speed and frequency are useful to control the measured responses used for crack detection in beam-like structures by the SAC.