A multiple mass broadband piezoelectric energy harvesting device is designed to broaden working band of the piezoelectric energy harvester, reduce its resonance frequency and improve the efficiency of conversion. The theoretical model of multiple mass piezoelectric cantilever beams is established to analyses the influence of the location of mass on the output power of piezoelectric cantilever. Then, the ANSYS is used to analyses the influence of the number of mass to the output voltage and resonance frequency of piezoelectric cantilever in ANSYS. An improved energy collection circuit is designed to compare with the classical circuit in this paper. Finally, an experimental system is built to measure the output voltage and output power of the piezoelectric cantilever beam. The experiment results show that with the increasing numbers of mass, the first resonance frequency reduced from 62 Hz to 28 Hz, the power increased from 17 mW to 31 mW, the working bandwidth increased by 39.3% and the output power of the new circuit is 1.31 times higher than the classical one. So we can know that with the increasing numbers of mass, the first resonance frequency reduced, bandwidth expanded, output power decreased and the new designed circuit has a higher conversion efficiency compared with the classical one.