During the harvest season, the harvested cotton is stored outdoor with the form of cotton module and protected by a module cover. Keeping the quality of those module cover which are repeatedly used is an important issue because the water-resistant ability of module cover may dramatically affect the quality of cotton. In our research, we try to develop an inspection system for the module cover to examine and quantify the quality of used module covers, more over, to predict the water penetration of it.With the images of sample cover, a method of damage recognition is developed. According to the result of experiment, the number of recognized pin holes on covers has a high positive correlation with the water penetration. Therefore, a prototype of inspection machine including PC, digital camera and back-lighting device is build. During the process of roll up the module cover, the system can automatically take serial images of it and analyze the defect shows in the image with image processing technology.