The invention provides a method for reducing heat and reheat steam temperature fluctuation of a boiler in a load increasing and decreasing process, and belongs to the technical field of thermal power generation. The problem of large fluctuation amplitude of the heat and reheat steam temperature of an existing boiler with an improved low NOx burner in the load increasing and decreasing process is solved. The method for reducing the heat and reheat steam temperature fluctuation of the boiler in the load increasing and decreasing process includes the following steps of A, recording operation data; B, carrying out a dynamic test to know the real situation; C, obtaining a theoretical value; D, correcting the theoretical value; and E, setting a parameter value. By means of the method for reducing the heat and reheat steam temperature fluctuation of the boiler in the load increasing and decreasing process, the fluctuation amplitude of the heat and reheat steam temperature of the boiler with the improved low NOx burner in the load increasing and decreasing process can be reduced, and safe and stable operation of a thermal generator set is guaranteed.