Abstract: In this paper, light intensity and temperature gradients were simulated in a climate incubator, to measure the decomposition rate of Sargassum vachellianum detritus and the contribution of seaweed detritus to inorganic nutrients in seaweed field. The purpose of this study was to provide scientific support for exploring the ecological service effectiveness of large seaweed detritus. The results showed that temperature had no significant effect on mass remaining and the decomposition rate of seaweed detritus (P>0.05); however, the effect of light intensity was significant (P<0.05). The mass loss rate of seaweed detritus was over 60% under different temperature and light intensity conditions in twomonth experimental period, and seaweed detritus decomposed faster under conditions of 25.15 ℃ and 3200 lx. Temperature had no significant effect on the release of nitrogen and phosphorus nutrients during seaweed detritus decomposition (P>0.05). Light had no significant effect on the concentrations of ammonium, nitrate and nitrite under the same temperature (25.15 ℃) (P>0.05), but had a significant effect on the concentration of orthophosphate (P<0.05). Light intensity had a significant effect on the concentrations of ammonium nitrogen and orthophosphate (P<0.05), and had no significant effect on nitrate and nitrite nitrogen concentrations (P>0.05). The cumulative contribution of dissolved inorganic nitrogen to waters was 4.597 to 17.321 mg·L^-1 and the dissolved inorganic phosphorus was 27.989 to 76.304 mg·L^-1 according to the amount of S. vachellianum detritus in study field. In conclusion, the amount of ammonium nitrogen and orthophosphate released from S. vachellianum detritus decomposition was higher than that of nitrate nitrogen and nitrite nitrogen under different temperature conditions. Higher temperature was more favorable for ammonium nitrogen release, while orthophosphate release was more favorable at low temperature. The release of nitrogen and phosphorus nutrients declined with the increase of light intensity, and the release of orthophosphate was inhibited with the increase of light intensity.