Abstract: Controlling of impurity type and content is a serious problem to be solved and faced by China grain distribution for a long period. The selective removal of dangerous impurities and reducing or preventing the damage caused by impurities to quality of grain druring storage are helpful to improve the storageablity and reduce storage losses of grain. Under the conditions of temperature (30℃) and relative humidity (80%－90%), the influences of sieve-through impurities on microbe activity and storage quality under the simulated storage condition were carried out in this paper. The results showed as follows: the sieve-through impurities had an indirect effect on storage quality of wheat by microbes. Under the suitable temperature and relative humidity, the sieve-through impurities made the microbes of wheat pile increase and resulted in wheat deterioration. The more microbes carried on the sieve-through impurities, the more rapidly the storage quality of wheat changed. The correlation analysis showed that the amount of external microbes and the detection rate of internal microbes had a significantly positive correlation with the fatty acid value (r=0.799, 0.602), and significantly negative correlations with germination rate and the activity of peroxidase. It is obvious that the sieve-through impurities have a great influence on the wheat storage quality. Therefore, the sieve-through impurities should be separated as much as possible before wheat warehousing in order to reduce harm of the impurities to wheat quality during storage and increase the wheat storage stability.