The regular characteristics of the transient response of a silicon-based PIN photodiode were stuidied experimentally, which irradiated by an ultrashort pulse picosecond laser, and the pulse response signals under different laser energy densities were measured. The analysis and experiment results show that with the increase of laser energy density, the device appeares a non-linear saturation state. The FWHM is from 37.2 μs to 113 μs, and the bottom width is from 181 μs to 322 μs. The impulse response signal has a broadening phenomenon, and the signal broadening means that the transient response of the device is degraded. At the same time, the analysis of the half-height width and the bottom width of the signal characteristics before and after saturation shows that whether it is an absolute increase or a relative increase, it can be seen that there is a more significant broadening phenomenon after saturation. It is caused by the attenuation of the speed on the falling edge after the device is saturated. Through theoretical analysis, the change in the concentration of injected photogenerated carriers affects the bipolar transport process, thereby changing the speed of the carrier transport process, resulting in degradation of the device response.