A photoelectric detection system based on a lock-in amplifier was developed. The noise charac. teristics of each part of the system, such as the photomultiplier, amplifier, and high-voltage power supply, were analyzed quantitatively. Research has shown that the ripple of the high-voltage power supply has a significant effect on system noise. Three high-voltage power supplies with different ripples were installed in the system, and the noise was analyzed. The results showed that in darkness, system noise was mainly contributed by photomultiplier anode dark noise and noise from the high-voltage power supply ripple linear. ly coupling into the system. In light, photomultiplier anode shot noise contributed the most to the system noise, and noise contributed by the high-voltage power supply ripple showed a positive correlation with both light current and ripple value. Based on the above findings, the transfer function of the high-voltage power supply was analyzed, and its feedback coefficient was optimized. A high-voltage power supply with high stability and low ripple(less than 5 mV)was designed. The signal-to-noise ratio test of the system showed that the signal-to-noise ratio could be significantly improved by applying self-developed high-voltage power supplies, which were 38% and 125% higher than those of other high-voltage power sources(ripples of 15 and 50 mV, respectively).