Objective · To observe the micro-structure changes in rat tooth movement process under different force values through Micro-CT dynamic observation. Methods · Fifteen SD adult male rats at the age of 8 weeks were divided into three groups randomly (n=5), with the left maxillary as the experimental side and the nickel titanium coil springs, fixed between the first molar and incisor where thrust augmentation was conducted respectively by 20, 50 and 100 gf (1gf=0.009 8 N) for continuous 14 d to it. Rat scanning in vivo through Micro-CT was carried out at day 0, 3, 7, 10 and 14 after force values were loaded on. The root resorption crater volumes and structure parameters for bone trabecula at different time points were measured. Results · Three days after thrust augmentation was conducted, root resorption crater volume for each group had a slight increase and an obvious increase occurred from the 3rd day to the 10th day, and then a slow increase happened 10 d later; from the 7th day to the 14th day, root resorption crater volume for 100 gf stress group was obviously greater than those of the other groups with statistical differences (P<0.05). With time for thrust augmentation passing by, bone volume fraction at the pressure side of alveolar bone decreased gradually and bone trabecula morphology became tiny and exiguous; besides, bone trabecula gap became narrow first and broad afterwards, and trabeculae trended to change from clintheriform to rhabditiform. Furthermore, alveolar bone resorption occurred in each stress group with consistent tendency. Conclusion · Different orthodontic force values all can cause root resorption, which experiences lag phase, rapid phase and stationary phase. Over-loaded orthodontic force induces more root resorption. During the process of the tooth movement, the pressure side of alveolar bones appears reconstruction and absorption, whose variation is not related with force degree.