As the output voltage of vibration energy harvester reaches peak point at resonance, the resonant frequency should be designed near ambient vibration frequency. To match the resonant frequency with ambient, single degree of freedom model was employed to analyze the vibration energy harvester with a cantilever and a tip mass. Piezoelectric micro prototypes were fabricated and tested, and the maximum error of resonant frequency was 6%. The resonant frequency of the prototype was adjusted 10.5 Hz by increasing mass. In order to approach ambient vibration frequency of 50 Hz, the resonant frequency of prototype was tuned from 58.7 Hz to 50.4 Hz, and the output voltage was increased 4 times.