Objective To investigate the dynamic changes in the anatomy of the anterior segment with and without accommodation in primary and middle-school students. Methods This was a cross-sectional study. Ultrasound biomocroscopy （UBM） was used to test 54 primary students and 55 middle-school students in Fuzhou. Some parameters related to the ciliary body， iris， anterior chamber angle and other relevant data were measured with UBM. Data were analyzed using a paired t test and independent-samples t test. Results Results for the primary student group without accommodation were as follows： the ciliary process distance （CPD） was 160.53±17.78 μm， ciliary body thickness （CT） was 90.01±34.30 μm， iris-ciliary process distance （ICPD） was 23.11±3.33 μm， iris thickness （IT） 1 was 35.95±6.60 μm and IT2 was 52.81±9.94 μm， trabecular ciliary process distance （TCPD） was 151.27±23.11 μm， θ3 was 39.23°±7.46°， and θ4 was 56.02°±6.75°. The results with accommodation were as follows： 187.62±15.44 μm， 74.23±19.87 μm， 19.78±2.69 μm， 30.34±5.83 μm， 47.11±6.71 μm， 131.55±20.02 μm， 31.68°±5.14°， and 50.39°±4.89° （t=8.45， 2.93， 5.72， 4.68， 3.49， 4.74， 6.12， 4.96， P＜0.05）. The respective results for the middle-school student group without accommodation were as follows： 214.64±15.25 μm， 99.13±17.80 μm， 27.92±9.00 μm， 40.72±6.43 μm， 56.57±9.13 μm， 176.82±28.06 μm， 43.73°±6.93°， and 60.15°±10.48°. Results with accommodation were as follows： 271.38±11.96 μm， 93.27±10.42 μm， 21.66±7.54 μm， 35.68±4.37 μm， 50.17±6.49 μm， 136.41±19.35 μm， 39.51°±5.28°， and 53.68°±9.12° （t=20.91， 2.03， 3.81， 4.63， 4.08， 8.47， 3.46， 3.33， P＜0.05）. There was a significant difference between these 2 groups with accommodation（in the same sequence， t=30.95， 6.10， 4.47， 5.29， 2.37， 7.70， 2.32， and 6.98， P＜0.05）. Conclusion The most significant change occurs in the ciliary body with near accommodation： muscle fibers contract， especially in the circular muscles， and move forward and inward to induce the suspensory ligaments of the lens to loosen， thus achieving intense accommodation. The response is correlated with age： the younger the child， the more intense the response.