With advancements in energy conversion and microelectronics, it has become increasingly feasible to effectively harvest ambient vibrational energy for powering low-power wireless sensor nodes. Piezoelectric energy harvesting offers advantages such as ease of integration, miniaturization potential, and immunity to electromagnetic interference. To enable stable, efficient, and sustainable energy harvesting for wireless sensor network nodes, this paper presents a self-powered parallel-dual intermediate capacitance harvesting (SPP-DICH) interface circuit. The proposed circuit realizes autonomous operation through a passive peak detector, eliminating the need for external power sources. Compared to conventional piezoelectric energy harvesting interface circuits, the proposed parallel-dual intermediate capacitance harvesting circuit features an optimized topology with enhanced performance characteristics. A theoretical analysis shows that the proposed interface circuit retains all of the original functionality while achieving self-power supply. A detailed charge transfer analysis derived from the circuit schematic calculates the harvested power collected by the SPP-DICH circuit. Furthermore, the SPP-DICH interface circuit has been validated through simulation. Using LTspice circuit simulation software, this study compares the SPP-DICH circuit with the standard energy harvesting (SEH) interface circuit and the synchronous charge extraction (SECE) circuit. Results show that, under identical excitation conditions, the output power of the SPP-DICH is nearly 25% higher than that of the SECE and nearly 265% higher than that of the SEH, achieving a maximum output power of 35.32 μW. The design ensures load-independent output power while maintaining self-powering capability.