Abstract: An optical sampling signal holding method for a photonic analog-to-digital conversion system, based on frequency response principles of sampling and holding, controls photoelectric conversion processes after photonic sampling to be equivalent to the signal holding effect in switch sampling, and converts sampled optical pulses into a special holding waveform, directly eliminating the time mismatch between back-end electronic analog-to-digital converters and optical pulses. The photoelectric conversion frequency responses in the invention do not lead to additional expenses on active devices and software, which greatly improves performances of the photonic analog-to-digital conversion system. The method is not limited by the number of channels, and can provide more reliable technical solutions for realizing a photonic analog-to-digital conversion system with high sampling rate in the future.