Based on the equivalent impedance analysis, a method is proposed to realize a coupled-field simulation study of piezoelectric energy harvesters of rectified interface circuits through an equivalent linear circuit. The method opens up opportunities for finite element packages to analyze, design, and optimize energy harvesters at a system level, either adding the capability of simulating rectified circuit interfaces, or reducing a nonlinear circuit interface simulation into a faster and more stable linear simulation that can be solved more conveniently. The nonlinear rectified circuit is replaced with an equivalent external linear circuit of two passive electrical elements in series. The types and values of the passive elements are explicitly determined for the standard AC-DC (SEH) and synchronized switch harvesting on inductor (SSHI) circuit interfaces. For validation, this equivalent linear circuit is applied to a bimorph beam harvester in ANSYS, and a system-level analytical approach is introduced which integrates two established analytical approaches. The agreement between the ANSYS results and those of the integrated analytical approach validates this equivalent linear circuit method and the integrated analytical approach.