In this research, the biological characteristics and life cycle of Sargassum fusiformis, including the sexual reproduction of its mature sporophytes, asexual reproductions of its rhizoids and lateral branches were comprehensively studied. The meiosis and mitosis of the eggs, sperm and fertilized eggs of maricultural and natural S. fusiformis in Dongtou coastal waters were recorded in detail. In addition, the growth, development and differentiation of organs such as rhizoids, stems (main stem and lateral stem), leaves (air-bladders) and receptacles (female and male), as well as the morphology and structure features of embryos, young and mature sporophytes of S. fusiformis were described. On this basis, the existing reproductive biology and life cycle of S. fusiformis were partially supplemented and revised. The contents about asexual reproduction of S. fusiforme lateral branches and sexual reproduction of young S. fusiforme sporophytes were supplemented, and the life cycle diagrams of sexual and asexual reproduction of S. fusiforme were redrawn. The results of this study laid a foundation for the study of the maricultural ecology and the reproductive rhythm of S. fusiformis, as well as the population reproduction and its relationship to environmental factors.