Abstract: Objective: To observe the pupil diameter changes of different diopter under different rays.Methods: To measure and analysis the pupil diameter of 1 263 subjects（2 526 eyes） under different rays as: scotopic situation,common ray and Orbscan-Ⅱ.The patients were divided into four different groups according to different diopters as : group 1:-0.75 to-3.00 D,group 2:-3.25 to-6.00 D,group 3:-6.25 to-9.00 D,group 4:＞-9.00 D.Results: The pupil diameter of different diopters which is measured under the scotopic situation is the largest,smaller when it is measured by Orbscan-Ⅱand the smallest under the common ray.The mean value respectively is: 5.82 mm,4.14 mm,and 3.52 mm.The difference of the pupil diameter under the three situation indicate that the disparity between the scotopic and the common ray is maximum,the disparity between the scotopic and the Orbscan-Ⅱis smaller,between the Orbscan-Ⅱand the common ray is minimum.The minimun difference of the pupil diameter under different rays always keep the largest in the low diopter group,and the pupil diameter changes is the most obvious under rays in the low diopter group.Conclusion: The pupil diameter of different diopters changes greatly under different rays,and it is a very important parameter to measure the pupil diameter in different diopter under different rays before the refractive surgery.