Based on the character of strong promoter of the fibroin gene and high level secretion of fibroin of Bombyx mori, we amplified the promoter of heavy chain gene (Fib-H) and its downstream signal peptide sequence (FibHS) by PCR. After that, we cloned the PCR product in pBluescriptII SK (+) to form the vector pSK-FibHS and analyzed its sequence. The sequence identity was 99% comparable to that of the reported sequence by Blast on line. Then we digested pSk-Ser-DsRed-PolyA with Sal I/Kpn I to get DsRed-PolyA DNA fragment and subcloned it into vector pSK-FibHS to generate a transitorily secretory expression vector pSK-FibHS-DsRed-PolyA. After identified the recombinant plasmid by restriction enzyme digestion, we transfected pSK-FibHS- DsRed-PolyA into BmN cells by liposome. From the cells transfected with the recombinant vector, what the red fluorescence could be detected verified that the recombinant vector could express DsRed in BmN cells transiently. Furthermore, when silkworm had been injected with the recombinant vector pSK-FibHS-DsRed-PolyA, red fluorescence could be observed in the lumen of silk gland of silkworm. The result indicated that DsRed expressed transiently and was secreted into lumen of the silk gland. Therefore, we supposed that the cloned sequence (FibHS) possessed signal peptide bio-function. Moreover, this study would lay a foundation for the research on secretory expression of exogenous gene by silk gland bioreactor.