The invention relates to a photoelectric detecting system, in particular to a stray light jamming resistance photoelectric detecting system based on digital phase locking. The system comprises a light source, a TTL signal generator, an optical modulator, a sensor, a pre-amplifier and a lock-in amplifier, wherein the TTL signal generator or the optical modulator perform modulation on the light source, a modulated modulation light source and stray jamming light are converted into output measuring signals and jamming signals through the sensor, the measuring signals and the jamming signals are transmitted to the lock-in amplifier after being amplified by the pre-amplifier, and the lock-in amplifier is set to be only allowed to be passed by the measuring signals with the same frequency characteristics as the lock-in amplifier. According to the system, the measuring signal-to-noise ratio can be remarkably improved, the measuring lower limit can be effectively expanded on the condition that the light source power is not increased, and the system is particularly applicable to a pollutant monitor with the weak measuring signals, and is also applicable to stray light suppression of other optical measuring instruments.