The piezoelectric beam can convert vibration-energy into electrical-energy， which solves the sensor power challenges for the running parts of rail vehicles. In order to explore energy generation characteristics of the piezoelectric beam， the bending moment equation of the piezoelectric beam is established according to the small bending deformation theory， and the electromechanical conversion model is obtained with the one-dimensional piezoelectric stress. By using the Nelder-Mead simplex algorithm， optimization parameters of bimorph piezoelectric beam are given. And the influence of materials， structural parameters and frequency on conversion efficiency is analyzed. The theoretical model is verified correctly by simulation and experiment. The results show that the energy generation efficiency of the beam decreases with the increase of the elastic modulus ratio； the beams with low elastic modulus metal have high power-peaks and low resonant-frequencies. the beams get max-power at the optimal thickness ratio， the beryllium copper is 0.213， and manganese copper is 0.261. Compared with the measured value， the deviation of the output voltage is less than 0.13 V， the relative deviation is less than 2.8%， the deviation of the output power is less than 0.024 mW and the relative deviation is less than 2.9%.