In order to explore the function of the rape miR1140, we cloned the premiR1140 gene from rape cultivated variety westar by PCR approach, and successfully constructed the plant expression vector of premiR1140 with vector pPZP212, and transformed into variety westar by agrobacterium tumefaciens mediated approach. (1) PCR identification indicated that 14 strains positive transgenic plants of BnamiR1140 gene over expressed have been obtained; (2) Phenotypic observation showed that leaf morphology and flower tube of positive strains do not mutate, plant height, length of main inflorescence, the number of principal inflorescences and the 1 000grain weight are all equivalent to the control. But there are 5 positive strains with BnamiR1140 transformed (T₀) expressed double main sequence phenotype, and the branch height lower than control, branching number increased significantly than control, make the whole effective pod number increase, single productivity increased by 26% than that of control, and other 9 strains positive strains were consistent with that of wild type rape phenotype. (3) T₁ field phenotype analysis showed that the total growth period of T₁ transmutation plant of 5 strains with 35S∷BnamiR1140 (T₀ generation) overexpressed was significantly increased by 9-14 d compared with the control group, and, of which there are four strains, their plant type variation genetic followed 3∶1 Mendel segregation law. The study speculated that BnamiR1140 may participate in the regulation of branching and development of oilseed rape.