AIM: To observe the causes of the low vision in diabetic patients after phacoemulsification with optical coherence tomography (OCT) . METHODS: Fifty patients(50 eyes) with low vision after cataract operation were examined by OCT, and the causes of low vision were analyzed. RESULTS: In 50 eyes, 23 eyes had macular edema, 15 eyes with diabetic retinopathy, 8 eyes with senile macular degeneration, 2 eyes with macular hole, 2 eyes with normal OCT images. CONCLUSION: OCT is a new technique of retinal tomography with high-resolution.It is very valuable in the early diagnosis of the causes of low vision in diabetic patients after phacoemulsification. Macular edema is one of the most important causes of low vision in diabetic patients after phacoemulsification.