The invention discloses a method and device for supporting a weak adhesion bond soft rock roadway. The method includes that step 1, a drilling machine is adopted for drilling holes; step 2, a reamer bit and a drilling stem are connected, and the bottom of a drilled hole is chambered; step 3, an anchoring agent and an anchor rod are placed in the drilled hole, the anchor rod and the drilling machine are connected, the drilling machine drives the anchor rod to rotate and stir the anchoring agent, after the anchoring agent is solidified, a chambering portion is full with the anchoring agent to form a solid structure in a reverse wedge shape, and the solid structure is used for fixing an anchoring section of the anchor rod; and step 4, a tray is arranged on top of the drilled hole, a nut is used for screwing a free end of the anchor rod tightly, and pre-tightening torsion meets design value. The device is a chambering reamer bit comprising a casing, a cutter and a cutter control device, wherein one end of the casing is a connector, the cutter is connected with the bottom of the connector in pivoted mode, and the cutter control device is connected with the cutter and controls the cutter to be screwed out from the casing or withdrawn. By means of the device and method, an effect of the anchor rod is good.