Abstract: Using finite element method, a threedimensional nonisothermal numerical model was established based on PTT constitutive equation for halfclub coextrusion processes. The Arrhenius equation was applied to express the temperaturedependent transport properties. The coextrusion process of two different polymer melts was simulated, and the key to the study was the influence of interface position at die entry (r value) on die swell and interface position. It showed that the secondary flow of the die exit was weakened, and the die swell ratio was reduced with increasing r value. The interface position was stable in the die and at the die exit when r value made the two melts entrance area equal， and the melt inlet volumetric flow rate was equal.

Key words: die swell process, non-isothermal process, viscoelastic melt, interface position, secondary flow