Soybean (Glycine max) is short-day (SD) plant. Flowering time is a key agronomic trait that determines the transition from vegetative to reproductive growth. The study on the expression and regulation mechanism of flowering time gene in soybean photoperiod control of flowering pathway is particularly theoretically significant for soybean genetic improvement. In this study, a dual-luciferase reporter gene system with the GmFT2a gene promoter as promoter sequence was constructed, and the method of Agrobacterium tumefaciens injection into tobacco leaves was selected to study the effects of long and short days on the activity of the GmFT2a gene promoter. The results of transient expression analysis showed that the GmFT2a promoter was strongly induced under the SD conditions in tobacco. Furthermore, analysis of the GmFT2a promoter sequence revealed several cis-acting elements, including G-Box, Box 4, GT1-motif and TCT-motif by PlantCARE search. It was speculated that these elements might promote the expression of GmFT2a gene in the SDs and played a role in promoting flowering. The results of this study provided a basis for a better understanding of the function of the GmFT2a gene and further exploration of the complex flowering mechanism of soybean.