The invention relates to a denitrification system and a method for sintering gas without an ammonia reductant. The system comprises a sintering machine, a heater, a denitrification reactor, a deduster, a fan, a desulfurization tower and a chimney, wherein the deduster, the fan, the heater, the denitrification reactor, the desulfurization tower, and the chimney are sequentially connected with the sintering machine. The denitrification reactor is connected to the sintering machine behind the deduster, i.e., the deduster, the fan, and the heater are sequentially connected between the sintering machine and the denitrification reactor. The denitration reactor is provided with a catalyst layer. The method comprises the following steps that: after being processed through the deduster, the sintering gas is heated to a appropriate temperature through the heater, and is send to the denitration reactor; the sintering gas is subjected to a catalytic reduction in the presence of a catalyst in the denitration reactor to remove NOx; after being dedusted and desulfurized, the reacted sintering gas is discharged in atmospheric environment. With the present invention, the ammonia reductant does not require; sources of the catalyst are extensive; price of the catalyst is low; investment and operation cost of the system are relative low. In the present invention, the ammonia reductant does not be adopted, a reduction component CO in the sintering gas is adopted as the reductant, such that a plurality of problems due to adopting the ammonia reductant are avoided.