Abstract: The transgenic Spirulina platensis constructed in our lab was cultured in a PhR-L20C photobioreactor designed by the Institute of Process Engineering,Chinese Academy of Science.The conditions were optimized and applied for the high-density cultivation within the parameters of this photobioreactor.The initial pH was about 9.0,light intensity 10000 Lx,and the temperature 28-30℃.The result showed that the average optical density(OD560) reached 3.0 after 10 days with a growth rate of 0.3 OD reading per day.The final average dry weight yield of S.platensis was 1.3 g·L-1.After cultivation for 30 days without the aid of the antibiotic,G418,in the photobioreactor,the target gene was positively detected by means of PCR on the genome of S.platensis.In addition,the Western-blot result proved the foreign gene was effectively expressed in the transgenic S.platensis.