The growth period and its genetic regularity of 49（7×7） three-line hybrid japonica rice combinations and its parents in Heilongjiang province was studied. The results indicated that the growth period of F1 was common effected by both parents, and was positive correlation either. The influence of parent with longer growth period was bigger than the shorter. The growth period of F1 could be longer than the shorter one of parents and the average of them.The growth period of F1 surpassed the parent with longer growth period when the difference less than 8 day. The growth period of F1 was between the average and the longer one when the difference between them more than 8 day, and close to the parent with longer growth period.