Samples of phlogopite-vermiculite (phl-ver) interstratified minerals from Weili mine, Xinjiang, have been studied. Using the single crystal sheets of phl-ver samples, the authors measured the basal spacing of seven phl-ver samples with X-ray diffractometer. The structure factors and the coefficient of variation (CV) of the basal spacing obtained were calculated. According to the result of X-ray diffraction analysis the samples of phlogopite-vermiculite interstrati- fied minerals might be divided into two groups: (1) the regular 1∶1 interstratified mineral of phlogopite and vermiculite layers, specifically called hydrophlogopite; (2) the segregated interstratified minerals of phlogopite layers and hydrophlogopite layers. The calculated and the observed structure factors for 001 diffractions vary similarly with the index 1. So the regular interstratified structure of ph1-ver is defined as a regular 1∶1 interstratified structure.