Abstract: Abstract: Increased phosphorus (P) losses from land to waterbody via runoff and drainage are one of the important factors causing eutrophication of surface waterbody. Flue gas desulfurization gypsum (FGDG) is a synthetic by-product generated from the flue gas desulfurization process in coal power plants. Due to the high Ca2+ content of FGDG it can potentially be used to immobilize P in soils. To study the effects of FGDG on soil P losses, not only to open up a new way of FGDG resource utilization, but also to enrich engineering technologies for controlling agricultural non-point source P load. In this study, soil column leaching experiment and artificial soil slope & rainfall simulation experiment were conducted to examine the impact of FGDG which came from one of Shanghai coal-fired power plant, on the leaching and runoff P losses from coastal plains soil of Chongming East Headland, Shanghai. Four mass rates of FGDG (0, 1%, 2.5% and 5%) were applied to soil column and two mass rates of FGDG (0 and 1%) applied to artificial soil slope. The results indicated that: 1) Ca2+ dissolved from FGDG transformed water-soluble P to insoluble P in soil, and turned Ca2-P, Al-P into Ca8-P and Ca10-P which were more inclined to fix in soil. Compared with the control group, the reduction rate of total dissolved phosphorus (TDP) loss of the soil columns applied with FGDG reached 92.8%-94.8% and there was no significant difference among three FGDG treatments (P>0.05). 2) FGDG significantly improved soil permeability and anti-erosion ability (P<0.05), 1%-5% FGDG made the saturated permeability of soil columns increase nearly 10 times, there was no significant difference among three FGDG treatments (P>0.05). Compared with the non-FGDG slopes, 1% FGDG addition achieved the maximum runoff reduction rate of 37.5%, the maximum reduction rate of sediment loss of 59.5%. It was indicated that much adsorbed P on suspended sediment was prevented from migrating along with surface runoff. 3) The reduction rate of TP loss of soil columns with FGDG addition was 23.6%-79.5% and ascended as the adding amount of FGDG increased. Up to 61.5% more TP was held in slope soil with 1% FGDG addition than the non-FGDG treatment. The ratio of TDP loss accounted for TP loss was only 0.6%-6.1%, reflecting enhancement of soil permeability and reduction of surface runoff and sediment loss were the primary mechanisms of FGDG to control P loss from soil, and the deposition reaction of calcium and phosphoric acid belonged to subordinate P-fixing mechanism. When the mass ratio of FGDG was more than 1%, the effect of FGDG on reducing the loss of soil P was not significant (P>0.05), which indicated that the effect of FGDG on soil P loss was also influenced by Ca2+ dissolution efficiency of FGDG, the TDP content and soil particle physical characteristics and other factors together. On the whole, using FGDG to control phosphorous losses from soil can achieve both resource utilization of desulfurization solid waste and reduction of water eutrophication risk due to P transportation.