Abstract: Eight factors influencing maize yield were studied by using grey system theory.The results showed that the order of each character of its relational grade decreases as follows:line seed number, 100-seed weight, ear length, plant height, ear line number, ear height, ear diameter, the days from sowing to flower.Eighteen maize cross combination was analysed, which was divided into three classes.At the same time, we have studied inbreds.The results indicated that zhong 31and P167 were better than others.In addition, the comprehensive application of grey system theory to maize breeding was discussed preliminarily.

Key words: Grey system theory , Relational grade, Maize breeding, Reference combination