Objective: To study the microstructure development of mandibular bone in rats on timing sequence and under different occlusal force. Methods: 63 male SD rats aged 23 days were randomly divided into three groups (n = 7): Baseline group, soft-diet (SD) group and hard-diet (HD) group. 7 rats were killed at week 0, 2, 4, 6 and 8 respectively after feeding the food with different hardness.Micro-CT was used to reconstruct and analysis microstructure of the region of interest in mandible of the rats. Results: Compared with HD group, bone volume/total volume (BV/TV) and trabecular thickness (Tb. Th) decreased significantly after 4 th week (P ＜ 0. 05), the bone surface/bone volume (BS/BV) and trabecular separation (Tb. Sp) increased significantly during the 4 th to the 6 th week (P ＜0. 05) . Conclusion: In the process of mandibular development in rats, reduction of occlusal force may lead to reduction of bone mass, and the changes of microstructure are closely related to the time of intervention.