Flour particle size distribution is a major factor affecting the milling behavior in common wheats (Triticum aestivum L.). Also, a previous study has revealed a relationship between flour yield and median flour particle size of Japanese wheats. However, the genetic base of Japanese common wheat is narrow and will need to be broadened. Therefore, in order to help develop the genetic resource for higher flour yields in Japanese wheat breeding, the flour yield of one hundred and seventy Chinese common wheats were investigated in relation to the median flour particle size and the flour particle size distribution patterns as determined by laser diffraction. The results showed significant differences in the median flour particle size and distribution patterns of Chinese wheats and the Japanese wheats that had been analyzed in a previous study. In particular, 45% of Chinese wheats were categorized as hard wheats, but only 4% as soft wheats. In contrast, the previously analyzed Japanese wheat proportions were 20% and 25%, respectively. The results show that analysis of median flour particle size distribution by laser diffraction is a simple but effective tool for measuring and selecting the good flour milling quality in Chinese wheat genetic resources. In addition, the major differences between the Japanese and Chinese wheats highlighted in this study occurred despite the fact that it is well known that Chinese common wheats contributed to modern Japanese wheat varieties. The differences may be explained by either the founder effect or by a selective bottleneck in Japanese wheat genetic resources.