Abstract: To investigate the distribution of dinoflagellate cysts and the relationship between cyst and motile cell,water samples and sediments both from TFO corer samples and from sediment traps were collected monthly at 4 stations in Daya Bay,South China Sea,from Dec. 1999 to Jan. 2001. A total of 31 different cyst types were recorded. Cysts of calcareous Peridiniales mainly Scrippsiella trochoidea were the most dominant species in surface sediments at four station, which occupied from 47% to 58%. While others only occurred within restricted periods scarcely. Results from experiment on sediment trap revealed that the highest production rates(up to 3.48105 cysts/m2d)was in late autumn,while the lowest in winter. A dense bloom of Scrippsiella trochoidea broke out from Aug. 2000 to Sept. 2000 in studied sea area,and significant high concentrations of its cysts including resting cyst and temporary cyst were observed. The highest production of temporary cyst happened during the period of the bloom. however,more resting cysts were produced at the end of the bloom. This result suggest that large encystment(both resting and temporary cysts)of Scrippsiella trochoidea appeared to result in bloom termination,while the high cyst concentration in surface sediment in Daya Bay provide richseed bedfor the motile cell in upper water column and also the possibility of the occurrence of bloom.