In order to improve air quality and reduce haze, Chongqing has raised the nitrogen oxide emission requirements of gas industrial boilers, reduced the emission limits, and promoted a large number of low-nitrogen transformations of industrial boilers in Chongqing. In this paper, the main generation mechanism of nitrogen oxides and different technical schemes of low nitrogen transformation were introduced. Six representative industrial boilers were selected to carry out low nitrogen transformation based on FGR technology, and nitrogen oxide emission under the reference oxygen content, smoke exhaust temperature, thermal efficiency and actual output of boilers before and after the transformation were compared and tested. The test results show that the actual output of industrial boilers can be reduced and the energy consumption of boilers can be increased by using FGR low nitrogen technology.