The present invention provides a method for detecting and classifying block edges from DCT-compressed images, and more particularly, a fast method for classifying the edge direction of each block in the DCT-compressed images. The method includes: extracting DCT coefficients by blocks constituting the compressed image; and applying an arithmetic operation defined for each direction component to the DCT coefficients, and comparing the results of the arithmetic operations to determine the edge direction component. The present invention is directly applied in the DCT domain based on the quantitative analysis on the contribution factor of each DCT coefficient to formation of the directional pattern of the block edge, thereby drastically reducing the computational complexity of arithmetic operations necessary to the detection and classification of block edges.