Abstract: In order to explore the characteristics and regulatory factors of decomposition of macroalgal litter, the decomposition process of the main and lateral branches of Sargassum horneri and Sargassum thunbergii, two dominant algae species in gouqi Island algal farm, was studied by decomposing mesh bag method. The results showed that: (1) the decomposition rate of lateral branches was faster than that of main branches, and the decomposition rate of different parts of Sargassum was faster than that of copper algae; (2) The N content of seaweed had different degrees of fixation and release in the decomposition process, the C content showed a downward trend in the whole decomposition process, and the P content had a rapid decay process in the early stage of decomposition, and gradually decreased with the decomposition process; (3) The results of correlation analysis showed that the contents of chemical components in seaweed and environmental factors had different degrees of influence on the decomposition rate of seaweed, and the water temperature had the most significant effect on the decomposition rate of seaweed, showing a very significant positive correlation (P < 0.01).