A novel triazine flame retardant (FR) has been successfully synthesized by the reaction of cyanuric chloride with sodium sulfanilate followed by diethanol amine. Its structure has been fully characterized by IR and 1H NMR spectroscopy. The effects of reaction solvent, acid-binding agent, reaction temperature, and molar ratio of starting materials on the yield of FR were investigated in detail. Experiments showed that when the molar ratio of intermediate I to diethanol amine is 1 to 1.2 in the presence of sodium carbonate as acid-binding agent in acetone-water at 45 ℃, the yield of the obtained FR reaches 81.4%. Thermogravimetry (TG) test indicated that the FR has good thermostability and char-forming ability. In addition, the flame retardancy and thermal behavior of the cotton fabrics treated with FR were studied by limiting oxygen index (LOI), vertical flammability test, and thermogravimetry (TG) to evaluate the flameretardant performance of the target FR. These results demonstrated that the flame retardancy and thermal stability of the cotton fabrics treated with FR were clearly improved.