A composite filter cartridge, comprising: a filtration assembly comprising a pretreatment filter cartridge and a fine filter cartridge disposed successively from outside to inside, the fine filter cartridge comprising a central water collecting pipe and a fine filtration membrane wound around the central water collecting pipe; a first end cap disposed to an axial end of the filtration assembly and connected to the filtration assembly to cover the axial end of the filtration assembly; a second end cap having a cylindrical shape, disposed to the other axial end of the filtration assembly and connected to the pretreatment filter cartridge; a taste filter cartridge comprising an activated carbon layer disposed in the second end cap, the taste filter cartridge being connected to the central water collecting pipe and being located downstream of the fine filter cartridge, a concentrated water channel and a circulation channel disposed successively from outside to inside and separated from each other being defined between the taste filter cartridge and the second end cap, the circulation channel being in communication with the central water collecting pipe and upstream of the taste filter cartridge, and the taste filter cartridge being provided with a pure water channel configured for the pure water outflow, a connecting casing disposed in the second end cap and connected to the central water collecting pipe, wherein the concentrated water channel is defined between the connecting casing and the second end cap, the taste filter cartridge is disposed in the connecting casing, and the circulation channel is defined between the taste filter cartridge and an inner wall of the connecting casing, wherein a part of the circulation channel runs adjacent to the taste filter cartridge; and a protruding block disposed between the inner wall of the connecting casing and the taste filter cartridge to make the inner wall of the connecting casing spaced apart from the taste filter cartridge, wherein a gap between the inner wall of the connecting casing and the taste filter cartridge constitutes the circulation channel. a filtration assembly comprising a pretreatment filter cartridge and a fine filter cartridge disposed successively from outside to inside, the fine filter cartridge comprising a central water collecting pipe and a fine filtration membrane wound around the central water collecting pipe; a first end cap disposed to an axial end of the filtration assembly and connected to the filtration assembly to cover the axial end of the filtration assembly; a second end cap having a cylindrical shape, disposed to the other axial end of the filtration assembly and connected to the pretreatment filter cartridge; a taste filter cartridge comprising an activated carbon layer disposed in the second end cap, the taste filter cartridge being connected to the central water collecting pipe and being located downstream of the fine filter cartridge, a concentrated water channel and a circulation channel disposed successively from outside to inside and separated from each other being defined between the taste filter cartridge and the second end cap, the circulation channel being in communication with the central water collecting pipe and upstream of the taste filter cartridge, and the taste filter cartridge being provided with a pure water channel configured for the pure water outflow, a connecting casing disposed in the second end cap and connected to the central water collecting pipe, wherein the concentrated water channel is defined between the connecting casing and the second end cap, the taste filter cartridge is disposed in the connecting casing, and the circulation channel is defined between the taste filter cartridge and an inner wall of the connecting casing, wherein a part of the circulation channel runs adjacent to the taste filter cartridge; and a protruding block disposed between the inner wall of the connecting casing and the taste filter cartridge to make the inner wall of the connecting casing spaced apart from the taste filter cartridge, wherein a gap between the inner wall of the connecting casing and the taste filter cartridge constitutes the circulation channel.