Due to the complexity of mold flow channel parameters, they have a significant impact on medical microtubule forming quality during the gas-assisted extrusion process. In this paper, the influence mechanism of mold flow channel parameters on medical microtubule forming quality is investigated. First, the multiphase flow model of the medical microtubule gas-assisted extrusion process is established. Then, the numerical solution of medical microtubule extrusion is presented based on Polyflow finite element software. Further, the medical microtubule size, morphology, velocity, pressure, and first normal stress difference under different mold flow channel parameters are compared and analyzed. Finally, the experimental platform for gas-assisted extrusion is built, and the correctness of the numerical simulation is verified by the extrusion experiment. The simulation and experimental results show that under the 15−5 condition, the inner radius, outer radius, and wall thickness of the microtubule are closer to ideal values, and the forming quality is better than other parameters. As the ratio of the gas-assisted to non-gas-assisted sections increases, the gas effect becomes more intense, and the shrinkage of the microtube increases. In the gas-assisted section, the wall thickness and outer radius of the microtubes increase first and then decrease, and they stay the same near the exit section. This reveals that gas-assisted forming technology can effectively eliminate extrusion swelling.