To study the life history processes and morphological traits of Sargassum horneri from the Sargassum seaweed bed of Gouqi Island,this study first conducted the investigation of the growth and reproduction during an annual cycle of Sargassum horneri,and 16 related biological parameters including individual length,blade,vesicle and receptacle were analyzed.Experimental results showed that growth of Sargassum horneri can be divided into 4 phases within the year according to the occurrence of different biological structures in its life history:(1) seedling period during July to August,during which plants consist of stalk,branch and blade briefly,plants grow with an average rate of 1.52 mm/d; (2) adult period during August to April of next year, all biological structures were consummated and successively recorded the occurrence of vesicle,secondary branch and receptacle in September,November and April of next year respectively,and plants grow with an average rate of 2.01 mm/d; (3) reproduction period during April to May,the occurrence of receptacles indicated the arrival of reproduction period,while the concentrated dispersion of ovums indicates the arrival of “climax” of reproduction period,and plants grow with an average rate of 3.80 mm/d;(4) senescence and degeneration period during May to June,the majority of plants begin ageing with detachment of biological structures,while the average growth rate of plants reaches 0.99 mm/d due to the supplement of immature individual.In the 16 biological parameters detected,10 parameters including length,individual biomass and primary branch length showed a significant seasonal variation(P <0.05).This warm-temperate species exhibited a phenological behavior intermediate between tropical and cold-temperate species of Sargassum. Analysis of within- and between-individual stability of 10 morphological parameters indicated the lowest stability of primary branch length(Ed=95),which belongs to the best parameters for distinguishing species and may provide us with the basis for morphology research and species identification of Sargassum.