The invention discloses a ceramic green body injection molding machine and a molding method thereof. The ceramic green body injection molding machine comprises a rack, a support, a mechanical arm, a direct pressure mold opening and closing device, a material feeding mechanism, a product conveying belt, a hopper, a molding mold, a plasticizing cylinder, a screw and a plasticizing motor; the support is vertically arranged in the middle of the rack, the molding mold and the direct pressure mold opening and closing device are arranged on the support, the material feeding mechanism is arranged at the bottom of the rack corresponding to the position below the molding mold, the plasticizing cylinder is horizontally arranged on the rack, one end of the plasticizing cylinder is connected with the material feeding mechanism, the other end of the plasticizing cylinder is provided with a hopper mounting base, one end of the screw extends into the plasticizing cylinder through the hopper mounting base, and the other end of the screw is connected with the plasticizing motor. Accordingly, the structural design is exquisite and reasonable, a traditional horizontal type is changed into a vertical type, the production efficiency is greatly improved, the produced product is good in compactness and smoothness, high in mechanical strength, high in humidity-state resistance value, not likely to break and high in product yield, and the production speed and the efficiency are high.