The three-layer co-extrusion blown film could combine a variety of different characteristics in the extrusion process and it can greatly reduce the cost, so the application of this multi-layer co-extrusion technology is more and more extensive. In this paper, the flow channel geometry of die for three-layer co-extrusion blown film was built and then meshed by ICEM CFD with all-hexahedral elements, and the die flow field numerical simulation was solved by POLYFLOW to analysis the interface shape and position for LDPE/HDPE/LDPE three-layer co-extrusion blown film. It shows that the interface fluctuates when each layer met in the co-extrusion channel. The differential pressure of two adjacent layers bring about interfacial deformation, interface position changes due to the flow channel rearrangement when each layer met the co-extrusion channel.