Abstract: The relation between a few main characters and the yield in the 7 winter-wheat cultivars was studied by means of the restrictive factors and the relational grade analysis of grey system theory. The results showed that the yield is more closely related with population, ear quantity and grains per ear, which are main character restrictive factors. The others are not character restrictive factors. Therefore, the colony is the most important. The winter-wheat colony is get reasonable at first in the growing, afterwards, ear quantity and grain per ear is assured by means of effective measures, which is the basis of winter-wheat high-yield.