Aluminum-silicon co-infiltration coating is usually sprayed on the surface of aeromotor blades which is at high temperature, so as to provide critical protection to prolong the service life of aeromotor blades. the thickness of the coating can be monitored through X-ray fluorescence non-destructive testing technology in a quick and expedient manner, but it is not accurate enough to detect the thickness of multielement double-layer aluminum-silicon co-permeated coating. Further the study of the relation between the thickness of multielement double-layer aluminum-silicon co-permeation coating and the X-ray fluorescence detection value. One method based on X-ray fluorescence nondestructive testing technology are proposed in this paper to reduce the error of X-ray fluorescence measurement. Moreover, the feasibility of the method will be examined by verifying the linear relation between the fluorescence pair value of Molybdenum and the thickness of the first layer. Lastly, based on the principle of X-ray fluorescence absorption and divergence, we will fit a computational model for the relation between the thickness of the intermediate layer and the fluorescence of molybdenum. We find the coating thickness of the experimental sample has a critical value, so that the relationship between thickness and fluorescence value is not monotonously increasing or decreasing. When the mass fraction of Molybdenum in the film is greater than that in the substrate, the fluorescence effect received by the instrument decreases first and then increases with the increase of the film thickness, with the critical value of about 14.3μm. The influence of interpenetration of elements on thickness measurement of Aluminum-silicon permeability coatings less than the critical value can not be ignored.