In order to meet the self-powered requirements of wireless sensor systems with vibration frequency varying in a certain range and limited space, a three degree-of-freedom vibration beam piezoelectric energy harvester with folded beam structure is designed. Based on the system structure and working principle, the theoretical analysis was carried out, and the finite element model of the folded beam structure was established. The finite element analysis and modal simulation are carried out. A prototype of the piezoelectric energy harvester with folded beam is fabricated, and the test platform was built and tested on the vibration table. The experimental results show that the theoretical analysis and finite element simulation results are basically consistent with the experimental results. Under the low frequency vibration of 3.5~8.5 Hz, the voltage greater than 5 V can be generated, and the maximum output voltage is about 17.5 V, which is 1.4 times that of the traditional single beam structure. Furthermore, it has three output voltage peaks and the working bandwidth is 4.5 times that of the traditional single beam structure. The effect of wide frequency is realized. The proposed piezoelectric energy harvester with folded beam structure can be effectively and adaptively used in low frequency and vibration frequency changing environments.