The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called Encoding Optical Coherence Tomography Angiography (En-OCTA) is presented, utilizing retinal Optical Coherence Tomography Angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia.