The slagging process is a popular problem in coal-fired power plants because the coal properties deviate from designed condition, at the same time, power plants is enduring a great pressure with the increasing of coal prices. Power coal blending provides an effective way to solve these two problems. In some traditional methods, blended-coal properties were usually treated by the weighted average method which induced the optimization solutions deviating from the actual results. The reason is that different coal property indexes are based on different benchmarks; for example, the sulphur content in coal is based on applied basis, while the slagging properties of blended-coal are calculated on air-dried basis, which was influenced by the contents of moisture and ash in each coal. In order to study the effects, based on the genetic algorithm, a model considering these two factors was build up to optimum the coal-blending scheme. Compared with the traditional weighted average method, the new model got higher slagging property indexes, as means the former method may include some coal blending schemes into the optimizing process, in which the real slagging parameters go beyond constraint standards. Therefore, in the case of coal-blending optimization to prevent slagging in furnace, these two factors are especially important and should be considered carefully to ensure the precise of slagging parameters, so as to obtain the optimum results both in the prices of coals and in slagging property.