Abstract：The constitution and the mechanism of the μCT225kVFCB micro-CT experimental system，which was co-designed by Taiyuan University of Technology，and Applied Electronics Institute，Academy of Engineering Physics of China，is firstly introduced. The maximum power and amplified factor of the system are 320 W and 400 times，respectively. It can perceive distinctly pores and fissures in rock specimens with size as small as 1–2 μm. It is a precise experimental system for intensive investigations on the meso-structure of either metallic or non-metallic materials. Series of dimensional triaxial meso-structure investigations on granite thermal fracturing under temperatures ranging from 20 ℃ to 500 ℃ were carried out with the system. It was demonstrated that the crystal grain size of the granite specimen is 100–300 μm with irregular shapes. The fracturing was developing with heating temperature increase. It was observed that certain micro-fissures in the specimens propagated under 200 ℃，and the micro-fissures developed and even connected to form larger fissures under 300 ℃. The length of the fissure could reach as long as 10 times against that under 200 ℃. A fissure net around each granite crystal grain was formed and made the polygonal grains be isolated with each other when the heating temperature reached 500 ℃. It was found that 90% of the thermo-fracturing happened along the weak boundaries between the crystal grains and the surrounding cement，with less than 10% of the fracturing fissures crossing the grains.
