Objective To investigate the effect of early mydriasis on pupil diameter in patients with diabetic retinopathy after cataract surgery.Design Randomized clinical trial.Participants 256 patients with diabetic retinopathy combined with cataract who un-derwent cataract surgery in Zigong Third People's Hospital from December 2020 to December 2021.Methods The patients were divid-ed into 128 cases each in the experimental and control group according to the random number table method.The experimental group was given compound tropicamide eye drops to dilate the pupil on the 1st to 7th postoperative days,and the control group was given di-lation on the 7th to 14th postoperative days.Pupil diameter≥7 mm at 5 min after the end of pupil dilation was considered to have reached the standard.Comparing the clinical data of the two groups,Logistic regression was used to correct the influencing factors of pupil diameter and analyze the correlation between the early pupil dilation and the diameter after pupil dilation.Main Outcome Mea-sures Pupil diameter and pupil diameter attainment.Results The ideal and total attainment of pupil diameter in the experimental group were higher than that in the control group(x2=9.976,P=0.002).After adjusted for age,duration of diabetes mellitus,diabetic retinopathy stage,preoperative corrected visual acuity,hemoglobin A1c(HbA1c)level,and albumin creatinine ratio(ACR)level,the pupil diameter after pupil dilation in the experimental group was greater than that in the control group(P<0.05).Early postoperative pupil dilation was independently associated with increased diameter after pupil dilation(OR=0.53,95%CI:0.38~0.71,P<0.001).Conclusion Early post-operative dilation is helpful to the better pupil diameter attainment and larger pupil diameters in the caract patients with diabetic retinopathy.(Ophthalmol CHN,2024,33:53-56)