The three-dimensional numerical simulation model of two polymer melts flowing through the traffic circle section path was founded. The coextrusion process of composite pipe was simulated used the finite element method. The stream line method was used to simulate the extrudate swell. Such simulated results as the location and shape of coextrusion interface, the shear stress profile were analyzed. It is found that the maximum shear rate occur near the convergence section of the outer polymer. The interface excursion is less than 1mm in the die path. As the melt flow out of the die, the interface excursion increase distinctly, the value is up to 6mm. The extrudate swell rate is 21% along the radial direction.