Abstract: Powder X-ray diffraction is one of the key analytical methods for measurement of material crystal structure and plays an important role in the studies on physics, chemistry, medicine, metallography, material science, engineering and technology, petrology and mineralogy. In this article several applications of powder X-ray diffraction in petrology and mineralogy, such as studies on rockforming minerals and clay minerals, petrofabrics, isomorphism and crystallinity measurement, were introduced. As the development of measurement technology, the new application expectation in research of mineral crystallization process, mineral surface property, quantity analysis of mineral phases and measurement of crystal structure of minerals were also put forward.