Continuous extrusion foaming of CO2 gas is an efficient method to produce microcellular. The CO2 concentration in polymer melt is related to initial bubble morphology. Using video recording in this paper bubble interfacial morphology was studied when the gas was injected into polymer melt . The process of single bubble formation in the static and dynamic polymer melt includes three stages. Screw was more effective for gas breaking up and separating. When mixed in screw channel, and blent in the mixing segment, the dispersion, and diffusion rate of gas into polymer melt were increased largely.