In piezoelectric energy harvesting, a synchronous charge extraction(SECE) interface circuit can be used to improve power conversion efficiency. Previous studies usually use additional displacement sensors and pulse power supplies, and the generated power is not enough for external devices to consume. In this paper, a novel self-powered multi-input interface circuit for piezoelectric energy harvesting using SECE(SPMI-SECE) and one shared coupled inductor is presented to effectively reduce the size and cost. Compared with the conventional standard energy harvesting(SEH) circuit, the proposed circuit has much better load adaptability. The working principle of this circuit is analyzed in detail. Simulations have been carried out to verify its performance.