An injection molding system includes an extruding system. The extruding system includes a mixing unit configured to receive the polymeric material from the melting unit and configured to mix a polymeric material with a blowing agent and to form a mixture, wherein the mixing unit includes a mixing rotor disposed in a hollow mixing cartridge, and a ratio of a shortest distance between an inner sidewall of the hollow mixing cartridge and the mixing rotor to a diameter of the mixing rotor is in a range of 1:1500 to 1:4500. The injection molding system further includes a discharging channel communicable with the extruding system, a molding device configured to receive the mixture from the discharging channel, and a supporting device configured to facilitate an engagement of the discharging channel and the molding device, the supporting device includes a first element protrudes from the extruding system and a second element disposed on the molding device.