Abstract: In order to compare the effects of different types of quenching circuits on the detection performance of 4H-SiC avalanche photodiodes (APD), single-photon detection experiments were conducted on two types of SiC ultraviolet APD by using passive quenching circuits (PQC) and active quenching circuits (AQC). It was found that during a long dead time in PQC, post pulse phenomena occur frequently, resulting in a higher dark counting rate (DCR) of APD, thereby reducing the signal-to-noise ratio of the device. A study was conducted on the time distribution of pulse probability after APD, and further analysis was conducted on the problems encountered by AQC in single-photon detection under higher device bias. A circuit improvement plan was proposed. The research results indicate that by adjusting the dead time of AQC to 45 ns, the device DCR can be reduced to 1/4 of the original level under the same single-photon detection efficiency. By effectively suppressing post pulse and accelerating APD recovery speed, AQC can enable the device to exhibit superior detection performance. This study provides a certain reference for the application of SiC APD in single-photon detection.