A composite filter-cartridge, a composite filter-cartridge assembly for a water purifier and a water purifier are provided. The composite filter-cartridge includes a pretreatment filter-cartridge, a fine filtration filter-cartridge and an activated carbon filter-cartridge arranged sequentially from outside to inside. The fine filtration filter-cartridge includes a first water collecting pipe and a fine filtration membrane. The activated carbon filter-cartridge includes: a second water collecting pipe, an outer circumferential wall of the second water collecting pipe except a lower end thereof and an inner circumferential wall of the first water collecting pipe being spaced apart from each other; and a activated carbon, lower ends of the activated carbon and the second water collecting pipe being in sealed connection, a water outlet hole being formed in the activated carbon and penetrating the activated carbon axially, and an upper end of the water outlet hole being closed.