Abstract: Inner ribs are thin-wall spacers, forming closed cellular structure to increase the stiffness of extruded profile. Rules to determine the clearance of die cavity, the length of flat portion of flow passage, and the way of supplying material to the inner ribs are formulated to guide the design of extrusion die. The software is implemented on SolidWorks2000 with the functions of self-extracting the dimensions of part from the input drawing file.