Corn (Maize L.) sib-Line hybrids and their improved hybrids were studied in several environments from 1986-1988. The result showed that sib-line hybrids enhanced 20% in the seed yield significantly. The main factars for the increased seed yield were due to the increases of stability, 100—seed weight and the nuber seed per row of the sib-line hybrids. The improved single-cross hybrid from sib-lines selected by the comparison possessed the same growth uniformity great heterosis as a common corn hybrid. The best genetic devergence and criterion as well as the characteristic compensation between the sib-lines remained to be studied.