Abstract: This study sought to investigate the optimum light intensity,cultivation density and the gametophyte advance development degree of Saccharina japonica,in order to provide technical support for gametophyte seedling.The suitable light intensity and cultivation density for the gametophyte advance development were determined by inspecting the female gametophyte development rate,ovulation rate and seminal vesicle formation rate.The suitable degree of gametophyte advance development was determined by inspecting the emergence rate and emergence time.It was found that the advance development speed of gametophyte under 37.5~62.5 μmol·m^-2s^-1 was significantly faster than that under 25.0 μmol·m^-2s^-1 in the condition of(13±1)℃ and 10.0 g·L^-1.The advance development speed of gametophyte in the density of 5.0~10.0 g·L^-1 was significantly faster than that in the density of 15.0~20.0 g·L^-1 in the condition of(13±1)℃ and 37.5 μmol·m^-2s^-1,and only partial gametophyte developed,some gametophyte grew filament in the density of 15.0~20.0 g·L^-1.The emergence test was carried out after the gametophyte was advance developed under the conditions of(13±1)℃,37.5 μmol·m^-2s^-1 and 10.0 g·L^-1.The emergence rate were over 96.0% after 5 days of cultivation when the gametophyte was advance developed for 11~12 d,while the emergence rate was 90.7% after 9 days of cultivation when the gametophyte was without advance developed,which was 4 days later than the advance developed gametophyte.As a result,the suitable condition of light intensity and cultivation density were 37.5 μmol·m^-2s^-1 and 10.0 g·L^-1 for gametophyte advance development of S.japonica,while the suitable advance development time was 11~12 d.