Under the conditions of ocean acidification, the increase of CO2 concentration in the environment has an effect on the dynamic change of the epiphytic bacterial community of Sargassum thunbergii. Specifically, the relative abundance of dominant epiphytic bacteria at phylm level and genus level varied in different ocean acidification conditions, indicating that ocean acidification changed the structure of epiphytic bacteria community. Under the conditions of ocean acidification, the cumulative effect of high concentration CO2 on the generation time-concentration of the epiphytic bacteria community was mainly through affecting the energy and material metabolism of the epiphytic bacteria community, and affecting its structure and function.