The invention discloses an image edge detecting method based on Fourier transformation. The method comprises the following steps: step 100, a black and white digital image I is obtained; step 200, Gaussian filtering is conducted to the image I, and then a filtered image Is is obtained; step 300, Fourier transformation is conducted to the image Is, and then frequency spectrum Fs of the Is is obtained; step 400, each frequency spectrum component Fs (km, kn) is multiplied by a phase shift factor so as to obtain a new frequency spectrum component, wherein km=0, 1, ..., M-1, and kn=0, 1, ..., N-1, the km and the kn are respectively wave numbers in the X direction and the Y direction, and x0 and y0 are respectively the offset amount in the X direction and the Y direction; step 500, an offset image Ib (m, n) is obtained after Fourier inversion transformation, wherein m=1, 2, ..., M, and n=1, 2, ..., N, and M and N are pixel numbers in the X direction and the Y direction; and step 600, the offset image Ib minus an original image I pixel-by-pixel, an absolute value Ie (m, n)=| Ib (m, n)-I (m, n) | is obtained, and the Ie is an obtained edge feature image. The method has the advantages of being high in calculating precision, fast in calculating speed and good in noise inhibiting ability.