It is difficult for the existing edge detection technology to eliminate the influence of noise and scratch on the edge detection, and maintain the clarity and continuity of image edge. An improved edge detection technique based on second order differential operator and mathematical morphology is proposed. Firstly, considering the morphological characteristics, the image processing method of open and closed morphological operation is improved to remove the scratches on the workpiece surface in advance. Then the edges of the workpiece are detected by the secondorder differential Laplace operator. Finally, in order to achieve better image denoising effect, a kind of enhanced denoising combining Gaussian and bilateral filtering is improved, and the final algorithm is verified by experiments. Experimental results show that the improved algorithm is effective in removing the surface scratches of the workpiece, and the edge clarity and peak signaltonoise ratio (PSNR) are greatly improved, laying a foundation for improving the workpiece identification accuracy.