Sargassum horneri is essential for the formation and diversity maintenance of the local marine ecosystem. Marine ecologists consider it a vital species for the reconstruction of seaweed fields and the restoration of marine ecology. In recent years, due to the dual effects of global climate warming and human activity intensification, the degradation of seaweed fields have become severe. However, the regeneration of macroalgae is an inherent characteristic that resists the effects of multiple disturbances and maintains the continuity of the population, affecting the distribution and spread of seaweed populations. To find out whether S. horneri can propagate new plants from the basal main branches or holdfast (i.e. whether S. horneri is a perennial) and whether it can continue vegetative growth after the main branches are broken and float. This study took S. horneri in the mussel culture area of Gouqi Island, Zhejiang province as the research object. Based on the fixed-point observation of the morphological characteristics of S. horneri, combined with the annual water temperature data, the study investigated its ability of vegetative reproduction and vegetative growth. The results showed that: (1) The plant height, trunk diameter and attachment area on the holdfast of S. horneri showed significantly seasonal changes (P<0.01). The temperature of seawater affected the survival of S. horneri holdfast. The temperature of about 25 °C was the critical temperature for the S. horneri holdfast to break and rot. When the temperature was higher than 25 °C for a period, the S. horneri holdfast would fall off and lose, and could not survive the summer for vegetative reproduction. Therefore, it was concluded that S. horneri in the mussel culture area of Gouqi Island, Zhejiang province, is an annual algae. (2) S. horneri exhibited the phenomenon of ‘top advantage’. The lateral branches of the damaged S. horneri rapidly grew, with the regeneration potential being greater near the cut or broken area demonstrating a pronounced ‘top advantage’ phenomenon. (3) The broken branches could regrow in the free-floating state, and the maximum average plant height increased from 23.08 cm to 180.07 cm in three months, and the average wet weight increased from 12.11 g to 644.59 g. The results provide a reference value for analysing the reproduction, diffusion and competition strategy of S. horneri. They also provide a scientific basis for the ‘golden tide’ source in the marine area near Zhoushan, Zhejiang province.