Abstract: Objective To evaluate the vessel density, flow index and foveal avascular zone of superficial and deep capillary plexus (DCP) in non-proliferative diabetic retinopathy (NPDR) patients with noninvasive optical coherence tomography angiography (OCTA), and explore the relationship between perfusion index and degree of NPDR. Methods Seventy patients with NPDR and 70 normal subjects underwent examination with OTCA. NPDR patients were divided into mild, moderate and severe group according to ETDRS grading Vessel density, flow index and foveal avascular zone (FAZ) were measured. Analyze the correlation between perfusion index and degree of NPDR. Results Parafoveal vessel density, parafoveal flow index, perifoveal vessel density and perifoveal flow index in the three NPDR subgroups were significantly lower than those of control (all P<0.05). Deep plexus perfusion indices were lower compared with superficial plexus (all P<0.05). Spearman's correlation analysis showed a negative correlation between severity of NPDR and superficial plexus perifoveal flow index, deep plexus parafoveal vessel density, deep plexus parafoveal flow index, deep plexus perifoveal vessel density, deep plexus perifoveal flow index (all P<0.05). Conclusion Deep capillary plexus perfusion index obtained by OTCA can be sued as a reliable tool to monitor the severity of NPDR.