Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system. A new idea is put up to design a quick single-photon detector. This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs). All of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the