The invention discloses a construction device for a cantilever scaffold and further discloses a construction method for the cantilever scaffold. The scaffold comprises vertical rods and cross rods which are fixedly connected to constitute a scaffold body. The construction device comprises concrete main bodies, structural steel and a pull rod; one end of the pull rod is connected with the upper portion of the corresponding concrete main body, and the other end of the pull rod is connected with one end of the structural steel; a steel plate is fixed to the other end of the structural steel; thesteel plate and the lower portion of the corresponding concrete main body are fixed through bolts; and the structural steel is horizontally arranged, and positioning rods are fixed to the horizontal surface of the upper portion of the structural steel and fixed to the vertical rods. Construction of the cantilever scaffold is simpler and more reliable, under the condition of decreasing of the length of the structural steel, the force-bearing condition of the structural steel is greatly improved, and the load-bearing effect of the structural steel is improved; meanwhile, the situation that moreholes are left in the concrete main bodies is avoided, and later-period repair work is reduced; and the situation that architectural structure construction in a building is not affected can be guaranteed, and the construction progress is advantageously accelerated.