The low porosity of the reservoir has a significant impact on the production of unconventional oil and gas, hence a device to increase reservoir porosity and enhance unconventional oil and gas recovery was developed. The device can be lowered to 3000 m and operate continuously for more than 30 minutes under a discharge voltage of 11 kV in the frequency range of 0–60 Hz to improve reservoir porosity by causing reservoir resonance. The equipment structure includes an energy storage circuit, trigger switch, and energy transducer. The theoretical model of the energy storage circuit was established by the state space averaging method to obtain the time constant which was verified by a simulation experiment. The gas spark switch with an adjustable gap was used, the frequency control of the discharge pulse was achieved by rectifier voltage regulation, and the underwater pulse arc fracturing experiment was performed to confirm the accuracy and stability of the frequency control. Additionally, the effect of frequency resonance on reservoir porosity improvement was examined through comparative experiments, and the images of the distribution of pore texture in shale obtained by the X-ray computed tomography (CT) system demonstrate that resonance excitation can significantly promote the development of fractures and the improvement of shale samples’ porosity. The stimulation operation field experiment was carried out on coalbed methane wells in Shanxi Province, and the multipole array acoustic logging image verified that the equipment has a good reservoir porosity improvement effect. Experimental results indicate that this study has a potential application value in the field of unconventional reservoir stimulation.