A new type of pin to be installed in mixing section of screw extruder is proposed based on the results of numerical calculation of flow field and local mixing efficiency. Two problems presented in general pin mixing section, i.e., the lack of randomization in mixing mechanism and the formation of dead spots, can be solved through diagonally-channeling pins from top to bottom. From the results of numerical analysis of local mixing efficiency it is known that in the cross-section of standard screw (in this study called ＇＇cavity＇＇) there are only small regions with high mixing efficiency which is mainly near the two upper corners of the cavity. If two pins are put into the cavity, large high mixing efficiency regions occur in the scope from cavity top to about 1/3 flight height. But, in the case of inserting two holed pins into the cavity, high mixing efficiency regions are distributed in nearly all over the cavity. It is impossible to get such useful information by experiments. Even though the calculation was confined in cross-section of pin mixing section, it has directive significance in designing the practical pin mixing section in the light of theory of distributive mixing.