The interface circuit is an important part of piezoelectric energy harvesting system.Classical interface circuits include Standard interface,SECE,Series SSHI and Parallel SSHI.In this paper, a new technique called SCEI is presented and its theoretical harvested power is calculated considering the constant displacement amplitude.The harvested powers of SCEI and four classical circuits are simulated and compared by using the electronic simulation software Multisim.The results show that the SCEI interface increases the harvested power,which is not influenced by the load resistance value,by almost up to 1.5 times compared with the SECE circuit.