Piezoelectric energy harvesting is an attractive technology for recycling energy from ambient vibrations. Many big challenges still limit applications for the piezoelectric energy harvester, including its low-power density and high operating frequency. Although many studies have been done on this topic, discussion continues. In this work, a modified piezoelectric cantilever energy harvester (PCEH) fabricated with (Ba0.85Ca0.15)(Ti0.9Zr0.1)O-3 ceramic was developed with a low operating frequency (20-40Hz) and a high-power density (1.5-2.0W/mm(3)). This ceramic presents a novel rhombohedral-orthorhombic-tetragonal multiphase coexistence, which is the origination of the enhanced piezoelectric response. A simple method is provided through optimizing the number of proof masses, which can be used to regulate the operating frequency of piezoelectric energy harvester. This discovery will be helpful in developing new piezoelectric energy harvesters with high-power density and low operating frequency.