The mature receptacles of Sargassum thunbergii were used as materials in this experiment. The effects of temperature(13~23℃), illumination (3 000~12 000lx) and photoperiod (15 L∶9 D, 12 L∶12 D, and 9 L∶16 D) on egg releasing and young sporophyte growth of S. thunbergii were investigated.It was found that it is conducive to releasing eggs at 20~23℃. Between 3 000~12 000lx, higher illumination was more favorable for releasing eggs. Photoperiod was not the main factor of affecting the egg releasing speed. Illumination was an important but not a key factor for the growth of S. thunbergii young sporophyte. Temperature was a key factor for the growth of young sporophyte. Temperature below 16 ℃ was not conducive to the growth of young sporophyte.