（1. Jiangxi Province Key Laboratory of Precision Drive & Control, Nanchang Instituteof Technology,Nanchang 330099, China）(2. Jiangxi Province Key Laboratory of Polymer Preparation and Processing, Shangrao Normal University,Shangrao 334001, China）
A 3D nonisothermal viscoelastic numerical model was found for a twolayer gasassisted coextrusion through the Cprofiled channel with PTT model describing the viscoelastic flow behavior of molten polymer and the simulation was carried out. The influence of melt inlet volumetric flow rate on die swell and secondary normal stress difference was researched and the relation between dying swell and secondary normal stress difference was investigated. The study results show that the melt swell ratio increases with its flow rate increasing and decreases with other melt flow rate increasing when two melts flow rate is not equal. The melt flow rate has little influence on melt swell ratio when two melts flow rate is equal. But the whole die swell ratio is always close to zero, whether the flow rate of the two melts is equal or not. In addition, the die swell ratio is proportional to the second normal stress difference in a gas-assisted coextrusion process.