In order to widen the working frequency band of the piezoelectric energy harvester based on cantilever beam, a novel electrical connection scheme was proposed. By dividing the surface electrode of the cantilever beam into the symmetrical regions, the positive and negative charge under the torsional mode could be effectively collected. Then the structural size of the cantilever beam was optimized to make the resonant frequency of the bending mode and torsional mode close, so as to achieve the purpose of widening the frequency band of the piezoelectric energy harvester. Finally, according to Erturk's distributed parameter electromechanical model, the output voltage and the natural frequency of two modes were studied. It was found that when the length-to-width ratio of the cantilever beam was within the range of 3.25 to 3.35, the first-order frequency of the torsional mode was close to that of the second-order bending mode, which realized the frequency band extension of the energy harvester. This work had certain reference significance for the research and application of the piezoelectric energy harvester based on cantilever beam.