The invention relates to a reconstruction method for a hearth three-dimensional temperature field. The method comprises the following steps that: a burning flame colorized image can be obtained through a CCD (Charge Coupled Device) image pickup system and a computer processing system, based on R,G and B pixels of a flame image, two-dimensional temperature of a burning flame image can be obtained through a neural network BP algorithm, an inverse solution of a radiative transfer equation can be combined, and three-dimensional temperature distribution of a burning flame in a hearth can be further obtained. The reconstruction method has the advantages of scientific design and creativeness, three-dimensional characteristic of coal dust in a large-scale boiler can be fully embodied, and the reconstruction method is significant to safety, economic benefit, clean operation and the like of the boiler. The system disclosed by the invention has the advantages of compact structure, less material consumption, long service life, stable and reliable performance, convenient for maintenance and high measurement precision of three-dimensional temperature, and flame combustion condition in the boiler can be controlled in time.