Abstract: Since the implementation of ultra-low emission in coal-fired power plants, the emission concentration and the ground concentration of gas pollutants have been reduced significantly. As a result, widespread concerns have been raised regarding whether it is still necessary to keep using high chimneys. The article studied the relationship between the chimney height and the maximum ground pollutant concentration of coal-fired power plant under ultra-low emission standards in plain areas. Particularly, the article investigated the building downwash under certain chimney height and explored the feasibility to optimize the height of the chimney. The results showed that since the implementation of ultra-low emission, the current recommended heights of chimneys for 300 MW, 600 MW and 1 000 MW generation units have decreased to 130 m, 140 m and 150 m respectively, while there is no significant increase of maximum ground pollutant concentration. Therefore, it is concluded that the magnitude of pollutant increase is acceptable without building downwash. Generally, the chimney height of coal-fired power plants under ultra-low emission in plain areas can be optimized and lowered further.