The invention relates to a method capable of effectively reducing nitrogen oxide in a coke oven. The method allows the point of blending of air and combustible gas in a vertical flue to move upward so as to delay blending combustion of the air and combustible gas. Specifically, for a coke oven utilizing lean gas for heating, a distance between a combustible gas inlet and an air inlet at the bottom of the vertical flue is allowed to be no less than 70 mm, or a nose bridge brick is allowed to be no less than 80 mm higher than the bottom of the vertical flue; for a coke oven utilizing rich gas for heating, the distance between the combustible gas inlet and the air inlet at the bottom of the vertical flue is allowed to be no less than 170 mm; and for a coke oven having been put into production and provided with adjusting bricks, the adjusting bricks should be closely arranged at two sides of the nose bridge brick. The method can effectively reduce the size of a high-temperature region at the bottom of the vertical flue, decreases highest combustion temperature and generation of nitrogen oxide in the vertical flue, and reduces nitrogen oxide in the chimney of the coke oven from the source.