The invention relates to a fractional flow reserve, in particular to a method for obtaining a fractional flow reserve of a blood vessel. The method comprises the following steps: A, receiving a bloodvessel image of an angiography unit, and processing the blood vessel image into sequence image data by taking time as a sequence; B, performing denoising processing on the sequence image data by usingnonlinear diffusion filtering based on a partial differential equation; C, segmenting the blood vessel image from the background image; D, performing wavelet edge detection on the blood vessel image,and extracting the edge of the blood vessel image by decomposing abrupt change points of the image; E, obtaining a blood vessel blood flow reserve score according to the blood vessel image and the time interval between every two frames of images. The invention aims to provide a method and a corresponding device which can avoid the possible wound risk caused by interventional diagnosis, and are short in consumed time and can accurately obtain the fractional flow reserve.