Coefficient of thermal expansion (CTE) and theoretical density of explosive crystal are significant properties, which affect the performance of explosives largely. XRay powder diffraction (XRD) is an important method to measure the CTE and theoretical density of explosives. The methods and principles for measuring the two parameters by XRD were described,and the experimental results of RDX and HMX explosive crystals obtained by density gradient method verified the reliability and accuracy of the method. It is proposed that the application of Xray diffraction should be strengthened in research of explosive crystal.