Cordierite ceramics were prepared by using talc, bauxite and kaolin clay as starting materials. According to the detected result of XRD step-scanning from 25° to 35° by a high temperature X-ray diffractometer, 2θ and d values of five peaks of cordierite crystal were ascertained. Then the least squares technique was used to calculate the crystal parameters: at 25 ℃, a=b=0.981 8 nm, c=0.927 4 nm, V=0.774 3 nm3; at 600 ℃, a=b=0.982 0 nm, c=0.926 2 nm, V=0.773 5 nm3. The crystal volumetric coefficient of thermal expansion (CTE) and linear CTE along  a and c axes were calculated, αV=2.33×10^-6 ℃^-1, αa=αb=3.27×10^-6 ℃^-1, αc=-4.19×10^-6 ℃^-1. The average CTE of cordierite crystal is as low as 0.78×10^-6 ℃^-1.