Use of the Xray diffraction method to measure microball coat thickness is studied. A mathematical model of Xray diffraction of microballs is created and solved using computer aided simulation. The relationship between diffracted X ray intensity and coat thickness is calculated with the help of a standard sample possessing a known thickness. The coat thickness of other samples can be calculated by the intensity of diffracted Xray based on the same condition. The experimental result shows that this method is a rapid, convenient, nondestructive means of measuring microball coat thickness.