Abstract: In order to improve the desulphurization performance of fly ash in flue gas, the dropper tube furnace was used, in combination with SEM, particle size analysis, XRD, XPS, thermogravimetric curve and chemical analysis and other methods, the authors investigated the effect of different sulfur-fixing agent dosage(calcium-sulfur ratio) on desulfurization performance of fly ash and combustion characteristics of pulverized coal. Meanwhile, the changes in the physical morphology, chemical composition and active calcium oxide content of fly ash were studied to verify the influence results. The results show that the ratio of calcium to sulfur has a certain effect on the desulfurization performance of fly ash and the combustion characteristics of pulverized coal. With increasing the ratio of calcium-sulfur, the sulfur fixation rate grows，the growth rate will be slow when calcium-sulfur ratio is between 0～1 and 2.0～2.5, fly ash desulfurization performance is enhanced. The desulfurization performance will be roughly the same when calcium-sulfur ratio is 3.0(excessive sulfur-fixing agent dosage) and 2.0 and 1.5. The proportion of large particle size of fly ash decreases,CaO and Ca(OH)2 content gradually increase, active calcium oxide content continues to increase, the trend will gradually diminish, when the calcium-sulfur ratio is in the range of 1.5～2.0. Active calcium oxide is a main component in the desulfurization’s reaction. The remain component of pulverized coal combustion gradually increase, and the calorific value is gradually reduced. The ash melting point initially decreases and then increases (the ash melting point will be the lowest position when calcium-sulfur ratio is 1.0, and the ash melting point will gradually increase when calcium-sulfur ratio is greater than 1.5. Based on the three factors, desulfurization performance, combustion characteristics and economics, 1.5 is the most appropriate rate of calcium-sulfur ratio.