NOVELTY - Co-producing sulfide based complex fertilizer by flue gas desulfurization, denitrification and decarburization, and coupling with phosphorus gypsum, comprises using ammonia as a coupling medium, performing wet flue gas desulfurization denitrification and decarburization of sulfide in the flue gas solution, transferring nitrogen oxide and carbon dioxide to a phosphorus gypsum suspension, forming gas-liquid-solid three phases, performing circulatory fluidizing conversion process to obtain a semi-finished slurry containing precipitated calcium carbonate and sulfur based complex fertilizer.    USE - The method is useful for co-producing sulfide based complex fertilizer by flue gas desulfurization, denitrification and decarburization, and coupling with phosphorus gypsum.    ADVANTAGE - The method can achieve pollution control and waste utilization; does not produce any waste and utilize other material; and has high economic value and resource and environment protection value.    DETAILED DESCRIPTION - Co-producing sulfide based complex fertilizer by flue gas desulfurization, denitrification and decarburization, and coupling with phosphorus gypsum, comprises using ammonia as a coupling medium, performing wet flue gas desulfurization denitrification and decarburization of sulfide in the flue gas solution, transferring nitrogen oxide and carbon dioxide in the flue gas to a phosphorus gypsum suspension, introducing ammonia gas to form gas-liquid-solid three phases, performing circulatory fluidizing conversion process to obtain a semi-finished slurry containing precipitated calcium carbonate and sulfur based complex fertilizer two products, where the number of moles of precipitated calcium carbonate is equal to number of moles of carbon dioxide absorbed from the flue gas, the number of moles of sulfur based complex fertilizer is equal to number of moles of carbon dioxide absorbed from the flue gas, the number of moles of ammonium nitrate is equal to number of moles of nitrogen oxide in the flue gas, the number of moles of ammonium phosphate is equal to number of moles of phosphate ion in phosphorus gypsum washing water; and in the flue gas desulfurization, denitrification and decarburization process, the process is carried out in a Venturi reactor at a temperature of not greater than 70 degrees C, the pressure of flue gas containing carbon dioxide and sulfide is not less than 20 kPa (gauge pressure), the flow rate of nitrogen oxide in the flue gas along the Venturi throat of the reactor is 20-40 m/s and the temperature is not greater than 15 degrees C, the mass % concentration of ammonia in low temperature ammonia-rich solution is 7-11% and is directly contacted with heat and mass transfer reaction, the liquid/gas volume ratio is 1.2/1000-3.2/1000, the flue gas temperature is reduced to less than 30 degrees C, sulfide in the flue gas is absorbed up to more than 95% and nitrogen oxides is absorbed up to more than 10%, and the vol.% concentration of carbon dioxide is reduced from 8-25% to less than 5%; using phosphorus gypsum acid washing water, passing into a countercurrent sprinkler line, spraying, bubbling and washing for 3 times, where the temperature of washing water is less than 20 degrees C, the volume ratio of spraying liquid/gas is 1/1000-3.2/1000, the molar concentration (mol/l) of sulfate ion, phosphate ion and fluoride ion in the spraying liquid are respectively 0.01-0.015, 0.01-0.025 and 0.05-0.09, the vol.% concentration of the tail gas residual carbon dioxide is less than 4%, the vol.% concentration of residual sulfur dioxide and nitrogen oxide are lower than 0.0048% and 0. 003%, and the residual ammonia content is less than 10 mg/m3.