The laminating-multiplying element (LME) with a high aspect ratio used in coextrusion process is highly desired since it has useful applications for the preparation of multilayer sheets or membranes. In this article, the flow behaviors of a polymeric melt through a high aspect ratio LME channel was simulated by the finite element method and verified by a coextrusion process. The results showed that the velocity Y distortion in LME lead to the interface deformation and the interface deformation can be improved by reducing the velocity Y gradient via decreasing the inlet flow rate or increasing the wall slip. POLYM. ENG. SCI., 59:973-981, 2019. (c) 2019 Society of Plastics Engineers