In order to understand the factors influencing limestone capturing sulfur during coal combustion and improving its capacity, a series of tests were conducted under different reaction condtitions. The results show that the relation between limestone desulfurization and Ca/S (mol/mol) ratio varies with reaction temperature. The capacity of limestone capturing sulfur arrived at optimum when Ca/S is 1.5 at constant high temperature of 1080 degreesC and the capacity of limestone capturing sulfur increases with temperature rising in the range of 25 degreesC similar to 1080 degreesC programmed temperature. The capacity of limestone capturing sulfur decreases with N-2 content increasing in reaction gases and increases with suitable additives adding to limestone. The raw samples and the residuals after sample combustion were analyzed by EA and TG-DTA techniques.