The invention discloses a measurement method of a coal dust and in-furnace heat flow mixing effect on the basis of a combustion image, and belongs to the technical field of thermotechnical measurement and image processing. The method comprises the following steps: firstly, carrying out edge detection on an unburned coal powder area in the combination image through an area first order difference algorithm with a fixed search direction, determining the mixing characteristic area of the coal dust and in-furnace heat flow, and carrying out block processing and gray level stage processing on the area. In the characteristic area, a gray parameter and a gray position distribution parameter which reflect a coal dust and in-furnace heat flow mixing situation are extracted, the gray parameter and the gray position distribution parameter construct a mixing coefficient which measurably evaluates the coal dust and in-furnace heat flow mixing effect, and therefore, the measurement of the coal dust and in-furnace heat flow mixing effect can be realized.