The invention discloses a DPS QKD (differential phase shift quantum key distribution) encryption system suitable for a GPON (gigabit passive optical network) system. The encryption system comprises an OLT (optical line terminal) and at least one ONU (optical network unit), wherein the OLT is formed by connecting a clock synchronization controller, a pulse coherent optical source, a 1:n beam splitter, a phase modulator and an adjustable attenuator in sequence; the ONU comprises a beam splitter, a beam combiner, a first single photon detector, a second single photon detector and a data acquisition card; the clock synchronization controller outputs two channels of electrical pulse signals; the first channel of electrical pulse controls the pulse coherent optical source to generate frequency of laser pulse; and the second channel of electrical pulse controls acquisition frequency of the data acquisition card in the ONU. The point-to-multipoint DPS QKD encryption scheme provided by the invention has the advantages of low cost, simple structure, high key generation rate and stable work performance, can implement point-to-multipoint key distribution and is suitable for the GPON system.