Abstract: Suckerrod is an important part in an oil well pumping system, Break down of sucker rod occurs rather frequently in some fields because of poor quality of products of some vendors. Repairing of the damaged sucker rod string causes increased work over and production costis. Thus analyzing the stress state of the sucker rod, and improving their metallograhic properties will be beneficial to prolonging the service life and lowering work over and production costs. In this paper, digital processing is applied to the photoelastic images of a plastic model of a suker rod coupling. This technique results in a high reslution of the photoelastic image and provides new information for image interpretation. The distribution of stress field, strain field, and displacement field in the work piece is obtained by digital processing of the interference fringe of the stress image to enhance accuracy. The stress distribution under the simulated loading condition is more clear and straightforward and is identified by different colors. Image processing techniques used include: image digitizing, image contrast enhancement by modification of the histogram, image color enhancement, false color density isolation, image feature extration, image addition, etc.