Abstract: In this paper, through the construction of recombinant E.coli BL21 ( PET-24 ( a +) -TtSBE) by genetic engineering method, the starch branching enzyme TtSBE from Thermus thermophilus was overexpressed.The enzymatic properties of TtSBE were studied.The results showed that the optimum pH of TtSBE was 6.5, the optimum temperature was 60 ℃, the half-life at 60 ℃ was about 40 h, and the specific activity of TtSBE was 773.27 U/mg after purification. By using 2% pyrodextrin as substrate, the TtSBE conversion temperature 60 ℃, pH6.5, the amount of enzyme 3000 U/g ( pyrodextrin) , after treated for 12 h, the content of the resistant component reached 50%, which was 7% higher than raw material. This study would lay the foundation for the further improvement of yield and quality of resistant dextrin.