Sargassum wightii is a common species in Weizhou Island of Guangxi, Xuwen of Guangdong and other sea areas, and is an economic macroalgae. Understanding the annual growth and early development of macroalgae can predict the mature time of thalli and provide scientific basis for artificial seedling and cultivation of macroalgae. This paper reports the annual growth characteristics, the effect of temperature on ovulation and the early developmental process of sexual reproduction of S.wightii living in the sea area of Xuwen, Guangdong. The results showed that the annual growth of S.wightii can be divided into 4 periods: fast growing period, mature period, decline period and resting period. The average length of thalli reached its miximum (188.32 ± 43.77cm) in early April, exceeding 180 cm in both April and May, and less than 5cm in late July to early November. The male and female reproductive parts of S.wightii are in the same receptacle, and the egg cell development belongs to 8-nucleui type. The culture temperature is very important to the ovulation process. Ovulation could not be achieved at 15, 27 and 30℃, but could be achieved at 18~24℃. The ovulation time was shortest at 24℃, only 3d. The zygotes developed into germlings with rhizoid buds at 24℃ for about 24h, and the seedlings developed a fourth leaflet after 30d of culture. The results of this study provide basic information for the biology, ecology, artificial seedling and cultivation of S.wightii.