The genetic model test of growing period of sorghum was Carried out by Augmented NC Ⅱ design.The results show the heredity of growing period of sorghum don not agree with additive──dominant model,and the dominant effect of gene is not significant. The ratio of distribution of the allele that control growing period is significantly different between sterile line and restoring line. For the heredity of growing period,the additive effect allele,a lateliness mature gene,is dominant,and the dominance is epistatic dominance.