Abstract: In this study, we cloned a full-length PHYA cDNA from the total RNA of tumours stem mustard, made a expression analysis in different organ and swelling development stage, then we constructed a overexpression vector and converted tumourous stem mustard through a Agrobacterium GV3101 by the calli dipping method. Finally, we obtained a transgenic plant that was validated by PCR.Compared with the WT tumourous stem mustard, the transgenic plant showed a conspicuous difference, dwarf stature, an early anthesis,deep green leaves and delayed stem swelling. According to these results, we presumed that PHYA gene may play an important role in the regulation system of stem swelling, and over-expression of PHYA may delay swelling development.