Aiming at detecting all the edge defects in the surface of strip steel，one way to select the structural elements is analyzed.A new edge detection method which combines multi-scale morphology with multi-structure element is proposed.Firstly，multi-scale morphological filtering method is used to get the edge of 4 structural elements;secondly，the image edge is extracted by some operations.Finally，the binary edge image is processed and the final result is obtained by edge thinning.The results show that the method solves the coordination problem between edge detection precision and denoising ability，the edges detail can be preserved well by extracting surface defect of strip steel edge at multiple scales，which establishes a basis for on-line inspection and automatic segmentation.