The invention relates to the field of sargassum horneri conservation, in particular to a method for measuring the releasing sargassum horneri cutting time. Linear relationships between the monomeric sargassum horneri diameter and the monomeric sargassum horneri mechanical strength and between the monomeric sargassum horneri weight and length are obtained as parameters; and on the basis of the parameters, a relationship between the sargassum horneri aging degree and the mechanical strength is determined to obtain cutting and seedling separation time in the sargassum horneri multiplication and releasing process. According to the invention, the sargassum horneri multiplication and releasing time can be measured precisely; and the blank of the whole sargassum horneri conservation field is filled. With the model, since the relationship between the sargassum horneri aging degree and the mechanical strength is determined, the scientific theoretical basis is provided for the cutting and seedling separation in the sargassum horneri multiplication and releasing process. Meanwhile, the high precision, efficiency and rapidness of the offshore in-situ cutting and seedling separation integratedoperation can be guaranteed; the economic losses caused by the aging of the sargassum horneri can be avoided; and the damages caused by sargassum horneri breaking due to the old branch aging are alsoprevented.