Abstract: In order to meet the requirement of the flexibility reconstruction projects in coal fired power plants, it is necessary to ensure the safe and stable operation of the units at low load. The low load SCR denitration is an important part of the flexibility reconstruction project. This paper analyzes why SCR reactor exits when the coal-fired boiler operates at low load, reviews the development of the SCR technology under full load, and introduces some typical retrofitting schemes to improve the adaptability of SCR at low load. These retrofitting schemes are compared with the original design from the aspects of initial investment, retrofitting schedule, effectiveness and other benefits. The specific situation of the plants or units should be considered as well. In addition, the alkaline sorbent injection technology is more practical in engineering, as it has some other benefits such as curing plume visibility, preventing the APH plugging, resolving equipment corrosion, reducing the desulfurization waste water and synergistic removal of heavy metals.