Piezoelectric vibration energy harvester is a new force (acceleration) - electrically coupled converter output device. In order to improve the output power and broad the operating frequency band of a single degree of freedom (SDOF) piezoelectric vibration energy harvester (PVEH), a two degrees of freedom (TDOF) broadband piezoelectric vibration energy harvester consisting of a SDOF PVEH and a spring amplifiers is proposed in this article. The finite element force-electrical coupled model is established by ANSYS software, and the effects of the model parameters (such as the mass ratio, the damping ratio, and load resistance, etc.) on the system vibration characteristics and electrical output characteristics are studied in detail. The results have shown that a larger mass ratio and a smaller damping ratio can both improve the piezoelectric cantilever energy harvester output power and broad its working frequency band, and a suitable matching resistor under short-circuit resonant condition can make TDOF produce larger output current, while one under open-circuit resonant condition can produce larger output voltage. After optimization, maximum power output of short-circuit resonance and open-circuit resonance reached 4386.5 mW/g2 and 4263.4 mW/g2, respectively. Band width of TDOF also reached 10 Hz,which was five times the size of SDOF.