The invention relates to an energy dispersion X-ray spectrum-based analysis method for phases of fly ash. The method comprises the following concrete steps: (1) analyzing chemical composition of the fly ash through a chemical process or X-ray spectrofluorimetry; (2) analyzing mineral composition of the fly ash through X-ray diffraction; (3) determining the kinds of elements requiring acquisition of images of power spectrum surface distribution; (4) acquiring backscattered electron images and element power spectrum surface distribution images of the fly ash and carrying out power spectrum point analysis on main phases; and (5) designing a phase analysis method, comprehensively processing the power spectrum surface distribution images of every elements in a same area and then removing noise in analysis results so as to obtain phase-split pseudo-color images and phase analysis results of the fly ash. The phase analysis method provided by the invention is effective to both crystalline and amorphous phases and sensitive to low-content phases. The method can be used for analyzing the kinds of phases composing the fly ash, calculating the volume percentage contents of the phases and observing spatial distribution of the phases.