The cable harness is widely used in electronic equipment and wiring component. Its quality can be measured by analyzing the length of wire inside diameter and outside diameter. The level set method is applied to segment the microscopic image of cable harness. To deal with adjoining object, we reset the RGB channels of the image and convert them to Lab space, where the level set method is applied to segment the inner counter. Lab space is selected for inner contour segmentation as it can enhance the difference between blue and yellow color information, which is an essential feature for this kind of microimage. Finally, the binary image is processed by mathematical morphology technique before obtaining the final internal contour. The experimental results show that the proposed method can obtain contours efficiently and make it feasible to the data extraction and quality control.