The invention relates to a low emission high efficiency grate-firing combustion device and a method. The method is characterized in that coal dust and a sulfur-fixing agent are fully mixed so as to enter into a grate-fired furnace through a hopper, a gas recirculation and spray water combined technology is utilized to rapidly pyrolyze coal dust so as to generate reducing gas, recirculation fume is utilized to carry the reducing gas and part of fine granule semicoke to enter into a recrudescence region in the furnace, and the combustion flow of the furnace is strengthened; and the purpose of reduction NOx is achieved, the no-burnout grains are continually combusted above a combustor, staged combustion of a fuel in the furnace is realized in a hearth, and meanwhile, and the combustion efficiency of the grate-fired furnace is also improved. According to the invention, the grate-fired furnace is introduced through a fuel staged combustion technology, on the one hand, the NOx and SOx discharge of the grate-fired furnace is reduced through combustion adjustment, namely, the NOx deprivation rate is 35%-55%, the SOx deprivation rate is more than 80%, thereby protecting an atmospheric environment; on the other hand, the combustion efficiency of the grate-fired furnace is improved by 1%-2%.