In order to optimize the response characteristics of PIN photodetectors to incident light signals, according to the carrier rate equation and considering the parasitic parameters of the chip and the parasitic parameters of the package, the equivalent circuit model of the photodetector was derived. In addition, the effects of reverse bias voltage, I-zone width, photosensitive surface, chip parasitic resistance and capacitance, package parasitic resistance, capacitance and inductance on the pulse response characteristics and frequency response characteristics of photodetectors were simulated. The results show that by increasing the reverse bias voltage, reducing the photosensitive surface and parasitic parameters (chip parasitic capacitance and resistance, package parasitic capacitance and resistance), selecting the appropriate I-zone width, , using the resonance effect of the lead inductance, it can suppress the waveform response to generate waveform distortion as well as improve the frequency response bandwidth.