Abstract: A measurement method of human nail fold microvascular diameter based on image processing technique was presented. First human microvascular image was obtained by microscopic optical amplification system and CCD digital image acquisition system. And then the contours and centerline of the microvascular were extracted with Hessian matrix after binarization of the image. The piecewise fitting of the perpendicular of centerline had been performed. The intersection point of contour edge and perpendicular had been calculated. At last the diameter distribution graph of the microvascular was obtained. The advantages of this measurement method were higher precision, fast and real-time compared with other measurement methods.