The invention relates to a coal composite sulfur fixing agent, belonging to the technical field of boiler combustion desulphurization. The composite sulfur fixing agent is made of the following raw materials in parts by weight: 40-70 parts of CaO, 5-10 parts of SiO2, 5-15 parts of Al2O3, 3-5 parts of Fe2O3, 0.5-1 parts of BaS, 0.5-1 parts of BaCO3, 0.1-1.5 parts of Zn, 0.02-0.05 parts of Cu, 0.05-0.1 parts of As, 0.01-0.05 parts of Pb, 1-5 parts of CaF2, 0.05-0.2 parts of MgO, 0.5-1.0 parts of TiO2, 0.5-1.0 parts of K2O, 0.1-1.0 parts of Na2O and 0.04-0.06 parts of Ag. The coal composite sulfur fixing agent of the invention can reduce the emission of SO2, the atmospheric pollution and the formation conditions for acid rain. Since pulverized fuel ash and coal cinder are converted to modified ash and can be used in cement production technology, the clinker production of common cement can be reduced generally, the mine resources and the energy consumed during cement production are reduced, and the emission of CO2 is reduced.