The interference of the harmonic emissions from molecules aligned at different angles can significantly modulate the spectra and result in the anomalous harmonic cutoffs observed in a recent experiment.The shift of the structural minimum position with decreasing the degree of alignment is also explained by this interference effect of the harmonic emissions.In this work, we investigate the delay-dependent harmonic spectra generated from non-adiabatically aligned molecules around the first half rotational revival It is found that the evolution of the molecular alignment is encoded in the structural minima.To reveal the relation between the molecular alignment and the structural minimum in the high-order harmonic spectrum, we perform an analysis based on the two-center interference model Our analysis shows that the structural minimum position depends linearly on the inverse of the alignment parameter .This linear relation indicates the possibility of probing the rotational wave-packet dynamics by measuring the spectral minima.