Abstract:The grain size of wheat flour is an important index to measure the quality of wheat flour.The on-line particle size detection is of great significance to guide wheat flour production.Commonly used methods for testing wheat flour particle size in laboratories，factors affecting the grain size of wheat flour and changes in wheat flour quality caused by two particle size classification methods were summarized in this paper.Differences in starch and protein components in wheat flour caused by changes in particle size was emphasized.The basic indexes such as whiteness，falling number and gelatinization temperature was changed with particle size.The changes in the quality of pasta products was also highlighted.