In this study, a self-powered synchronous asymmetric voltage flip and charge extraction (SP-SAFCE) circuit is designed.The circuit combines the features of parallel synchronized switch harvesting on inductor and synchronous electric charge extraction to achieve a function that completely flips the voltage polarity at positive peaks and completely extracts charge at negative peaks.Compared with conventional piezoelectric interface circuits, the SP-SAFCE circuit has the advantages of a self-powered peak detection module and switch, no rectifier bridge, and no requirement of impedance matching.Comparison experiments are conducted under varying conditions of driving frequency and distance between magnets.It is proved that under the same shock excitations, the SP-SAFCE circuit operates at a voltage 0.8 V lower than that of the synchronous electric charge extraction circuit, and its output power is approximately 1.15 times that of the synchronous charge electric extraction circuit, which makes it suitable for use as the interface circuit for a piezoelectric harvester under shock excitations.