Optical coherence tomography (OCT) is a non-contact imaging modality with advantages of high resolution and high acquisition speed. OCT can provide three-dimensional image structures and detect motion information in the samples. In this study, a high-resolution spectral OCT angiography system was constructed with the lateral and axial resolutions of about 6.7 μm and about 4.7 μm, respectively. The line scan camera was operated at 140 kHz and could complete a three-dimensional scan within 2 s. Based on this, the blood flow perfusion information was extracted by differentiating the adjacent B-scan images. A micro-vasculature network image of rat cerebral cortex was obtained. The experimental results demonstrate that the proposed system is suitable for capillary imaging.