Abstract: In order to find ideal natural depressors of preharvest sprouting in wheat, the experiments were carried out, i.e. searching them from chaff, spike-stalk, leaf and stem in ripen wheat plant and other foliages. The results were as follows: these four sorts of organs all contained germination inhibitors, but they had low restraining function. YSR was obtained from other foliages, and its function effect was obvious. YSR appropriate application concentration of restraining grain germination was 240g/l. Extracting one day was enough. Interaction didn’t exist between YSR and wheat varieties.