Converting vibration energy from environment energy into electrical energy for low power electronic products by using piezoelectric vibrators was one of the research hot spot in recent years. The geometric shape had a great impact on the generating capacity of piezoelectric vibrators. In this paper, the analysis models were established to simulate the influence of the change of the free end size for the output voltage and frequency of piezoelectric cantilever beam by using ANSYS software. The research results showed that there was some sort of the free end size, which made the energy from environment energy of low frequency vibration maximum.