Objective To study the relationship between diabetic corneal neuropathy and diabetic retinopathy (DR) in patients with type 2 diabetic mellitus (T2DM). Methods A total of 58 T2DM patients (58 eyes) complicated with or without DR who were admitted to our hospital from Mar. 2017 to Aug. 2019 were selected for the study (case group), including 16 patients (16 eyes) with no diabetic retinopathy (NDR), 21 patients (21 eyes) with non-proliferative diabetic retinopathy (NPDR), and 21 patients (21 eyes) with proliferative diabetic retinopathy (PDR). Fifteen healthy people (15 eyes) without diabetes mellitus with similar ages were selected as controls (healthy group). Both the case group and the healthy group were examined by corneal confocal microscopy, and the images were analyzed quantitatively to compare corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), and corneal nerve branch density (CNBD). Results CNFL, CNFD and CNBD of NDR, NPDR and PDR patients in case group were significantly lower than those in healthy group (all P<0.01). In case group, with the progression of DR, CNFL and CNFD gradually decreased (P<0.01, P<0.05). There was no significant difference in CNBD between NDR patients and NPDR patients (P>0.05). CNBD in PDR patients was significantly lower than that in NDR and NPDR patients (P<0.01, P<0.05). Conclusion Under corneal confocal microscope, the corneal nerve fiber damage in patients with T2DM appears earlier than DR, and it is related to the degree of DR, which can provide guidance for the diagnosis and treatment of DR.