X-ray diagnosis technology based on crystal diffraction is an important method to obtain key state parameters in the research fields of X-ray spectroscopy diagnosis, material analysis and structural characterization on high energy laser devices and synchrotron radiation devices. The calculation of crystal diffraction efficiency based on the dynamical diffraction theory and the design of spectrometer structure based on different focusing schemes are the two main interests in the research of the X-ray crystal spectrometer. In this paper, the evolution and latest progresses of classical crystal diffraction theory such as X-ray dynamical diffraction theory and diffraction calculation method for different crystal objects are summarized and discussed. The diffraction focusing characteristics, development, and application of X-ray crystal spectrometers with different geometries are discussed, and the X-ray crystal diffraction theory involved in the X-ray crystal spectrometer and the innovation and progresses of the focusing characteristics of various spectrometers, as well as the overall development trend, are comprehensively expounded.