Objective： To study the influence of occlusal force change on apoptosis of periodontal ligament fibroblast （PDLF） and expression of proliferating nuclear antigen （PCNA） in the fibroblasts, so as to explore the possible mechanism for remodeling of periodontal ligament. Methods： Animal model of occlusal force change was established by extracting the right first, second and third maxillary molars in male SD rats. The rats were sacrificed at 6, 12 hours and day 1, 2, 3, 5, 7, 14, and 28 d after extracting the teeth（n = 6）, and their alveolar bone tissues were harvested. H-E staining was used to observe the morphologic changes of the alveolar bone tissues. TUNEL method and immunohistochemistry were used to detect apoptosis and PCNA expression in PDLF. The rats with normal occlusal forces were used as control（n= 6）. The results were assigned a mean score based on the percentage and the intensity of cells positively stained for TUNEL and PCNA. Results：Animal model of occlusal force change was successfully established, H-E staining showed that the control group had more pycnotic periodontal ligament, orderly fibres, and flatter alveolar bone than the model group. TUNEL result showed that the cell apoptosis reached its peak at 12 haffer extracting the teeth （252.67 ± 6.62）, significantly higher than that of control group （7.17 ± 2.32, P〈0.01 ）, then gradually decreased to normal level on day 28 after extraction （8. 50 ± 1.87）. Immunohistochemical staining showed that the expression of PCNA had a similar tendency of apoptosis：PCNA expression peaked on day 3 after extraction （246.00 ± 7.21） and then gradually decreased to normal level （5.67 ± 2.16, P〈0.01）. Conclusion： Changes of occlusal force can facilitate the PDLF apoptosis and promote PDLF proliferation, contributing to the remodeling of periodontal ligament