Abstract: The paper introduces the design and operation of Shanxi Guofeng 300 MW ultra-low emission subcritical units burning low calorific coal. The principles and the application of the pollution controlling technologies are discussed. In this project, in-furnace desulfurizationand semi-dry flue gas desulfurization are used to control SO₂, the low-nitrogen combustion technology based on the state specification theory and SNCR to control NO_x, and bag filters to control powder . The results show that the boiler runs steadily and efficiently. The thermal efficiency at full load is 90.61%. The SO₂, NO_x and dust emission concentration at full load are 18.75 mg/m³, 40.30 mg/m³ and 4.9 mg/m³, respectively, all of which meet the ultra-low emission standards. The results indicate that the low-NO_x combustion combined with ultra-low emission technologies is applicable.