Abstract: In order to analyze the genetic mechanism of growth period and provide the theoretical supports for breeding in broccoli (Brassica oleracea L. var. Italica), six generations (P1, P2, F1, B1, B2 and F2) derived from two morphologically dissimilar broccoli inbred lines were used for genetic analysis of growth period trait based on mixed major gene plus polygene inheritance model. We designated the growth period as the days from field planting to flower buds emergence in this experiment. The results showed that the mean values of F1 lied between two parents but it was much closer to the high valued parent in growth period traits. Meanwhile, the growth period traits were controlled by two additive-dominant-epitasis major genes (B- 1 Model). The major gene heritabilities of B1, B2 and F2 populations were 44%, 59% and 56%, respectively. And the major gene heritability was relatively moderate and was influenced by environment significantly, which could be used in the selection of early generation in broccoli.