For attenuating the vibration of vehicle subframe with changing target frequency, a piezoelectric cantilever phononic crystal (PC) and its adaptive modulation strategy are investigated in this paper. Firstly, based on the cantilever-based PC structure, the bandgap characteristics are obtained by vibration transfer calculation and piezoelectric constitutive modeling. Taking the parametric analysis results of structural dimensions and the targeted vibration frequency intervals required by vehicle subframe, the experimental design of the piezoelectric cantilever PC is further carried out. The modal experiments indicate that two local resonant bandgaps and one electromagnetic oscillation bandgap appear in the solved frequency interval, and are both in great consistency with the theoretical calculations. Finally, an adaptive bandgap modulation strategy is proposed with controlling shunting circuit parameters, and the execution results show that the PCs employed to the vehicle subframe can effectively achieve vibration attenuation from the powertrain systems. Starting from experimental design and adaptive modulation of the cantilever PCs with piezoelectric materials, this research presents a novel framework for the application of acoustic metamaterials in vibration mitigating of automotive structures.