The invention relates to a composite slaked lime desulfurizing method and a device thereof. The method comprises the following steps: 1) blowing slaked lime into a smoke pipeline connected between a boiler and a bag-type dust collector to ensure that the slaked lime is mixed with smoke from the boiler; 2) humidifying the mixed smoke; 3) blowing the humidified smoke into the bag-type dust collector to ensure that gaseous sulfur dioxide molecules and the slaked lime perform a desulfurization reaction and are solidified; 4) clean smoke is exhausted to atmosphere from a gas outlet of the bag-typedust collector; and 5) filtering the solid, generated by smoke desulfurization, the slaked lime and the dust in the smoke by the bag-type dust collector, and discharging the solid, the slaked lime and the dust from a dust outlet of the bag-type dust collector. The invention also provides a composite slaked lime desulfurization device for realizing the method. The invention is the process and the device integrated with desulfurization, dust removal and pneumatic transmission. The device not only has small floor area, small investment, simple operation and stable running, but also fulfills the requirement of national environmental protection on emission standard of environment and atmosphere pollution.