A new type of pin to be installed in the mixing section of a screw extruder Is proposed based on the results of numerical calculation of flow field and local and integral mixing efficiency in the cross-section of a pin mixing section. Two problems presented in general by pin mixing sections, i.e. the lack of efficient mixing mechanisms and the formation of dead spots, can be solved by channeling pins from top-front to bottom-rear. The calculated results of local mixing efficiency indicate the location of regions of good or poor mixing in the cross-section of the mixing section, and the integral mixing efficiency provides the means to compare the mixing performance of different mixing sections. The experimental results of flow visualization and mixing pattern agreed well with those obtained from numerical calculations, thus supporting the validity of the theoretical analysis. Even though the study was confined to the cross-section, it has directive significance in the practical design of pin mixing sections in the light of the theory of distributive mixing.