The utility model discloses a multichannel conversion rapid pressure relief device for a drilling pressurized-water test. The core tube comprises a lower core tube sleeve connecting port, a middle core tube sleeve connecting port, an upper core tube sleeve connecting port, an upper core tube hole and a lower core tube hole, wherein the upper core tube hole and the lower core tube hole are formed in the core tube; a gland is arranged at the top of the core tube sleeve, a plug connector is arranged at the bottom, a first connector communicated with the core tube sleeve is arranged at the upper end of the plug connector, and a second connector is arranged at the lower end; the upper end of the core tube extends upwards out of the gland, and the lower end of the core tube extends downwards outof the core tube sleeve and is positioned in the plug connector; a sealing piece is arranged between the core tube and the core tube sleeve; an upper core pipe sleeve connecting opening, a middle core pipe sleeve connecting opening and a lower core pipe sleeve connecting opening are sequentially formed in the sealing piece from top to bottom, and a core pipe sleeve drainage hole communicated withthe drill hole is formed in the core pipe sleeve. The utility model has the advantages of simplified pipeline device, reliable capsule water stop, quick and complete pressure relief of the capsule, convenience and the like.