Abstract: This article reported a numerical simulation for the gas-assisted co-extrusion process of profiles with an L shape by a finite element method under the consideration of the gas layer as an actual flow. The simulation results indicated that the gas groove on the surface of the extrudates could be avoided when the gas entry location of the die was reasonably designed regardless of a high gas pressure. The gas-assisted co-extrusion die with an L-shaped profile was designed based on the previous studies and simulation results, and then an experimental investigation was carried out by use of the improved co-extrusion die. The experimental results confirmed that the gas groove on the surface of the extrudates could be avoided when the gas entry was located at a 5 mm position after the two melts converged. The experimental results were in good agreement with simulation results and also verified the rationality of the structure for this improved die accordingly.