摘要： The parameters of the two-stage synchronization algorithm for the auto-compensation quantum key distribution (QKD) systems are investigated. The synchronization algorithm does not provide for splitting a frame equal to the period of the optical clock to the time windows. The equipment operates in the search mode for receiving a photon. The equipment goes into test mode when receiving a photon. The reception of a photon in the test mode is possible only during the action of the strobe pulse. The rest of the time the channel does not react to photons and dark current impulses (DCI). The algorithm provides for sequential testing of frames with a stop at registration of the first photon. The algorithm makes a decision about the absence of a signal after a specified number of tests. The proposed algorithm makes it possible to use single-photon avalanche photodiodes (APDs) with a significant time delay between the moments of photon reception and the restoration of APD. Formulas for calculating the time characteristics of the synchronization algorithm in the search and test modes are obtained. A time of synchronization is obtained. A method for calculating the design parameters of the two-stage single-photon synchronization for a QKD system is proposed.