Recently, nano-composites that polymers are reinforced with nano-fillers have been developed to obtain further mechanical properties and further functionalities. However, intended properties of nano-composites have not been achieved because nano-fillers aggregate in the polymer. Therefore, it is important to understand and control the state of nano-filler aggregations. One of the production processes of nano-composites is melt extrusion with co-rotating twin screw extruder (TSE) which is superior in terms of productivity and mixing performance. Generally, dispersibility of nano-filler is changed by the geometry of screw segments and operating conditions of TSE. Then, we took notice the “Blister Disk” which had many holes on the seal ring segments of TSE. The feature of Blister Disk is that the dispersibility of nano-fillers is improved by extensional effect because the material is stopped at the Blister Disk and concentrated into the holes. But, the influence on the mixing performance by changing the geometry of Blister Disk have not been investigated as far as we know. Then, our objective is the optimization of Blister Disk geometry, like hole numbers, hole diameter and disk length. Firstly, as the solution of optimization of Blister Disk geometry, the state of flow at the Blister Disk was investigated and the mixing performance was evaluated by mixing index with 3D numerical analysis. Secondly, to validate the result of simulation, we chose the polypropylene reinforced multi-walled carbon nanotube (PP/CNT nano-composite) as the model of nano-composite and actually made it for evaluation of dispersibility. The dispersibility of PP/CNT nano-composites were evaluated by observation of PP/CNT morphology and measurement of the electrical conductivity for each geometries.