Abstract: Ferrographic monitoring technique is widely used in engineering nowadays,the main shortcoming of this monitoring technique is that the quantitative indexes can not indicate the monitored equipment's wear deterioration extent directly.So a new ferrographic quantitative index,deterioration index,is put forward to remedy the defect in this paper.The advantage of deterioration index is that the index makes the monitored equipment's wear extent become more perceptible and more comparable.In order to avoid thee one sidedness of using only one index to decide the wear extent,a comprehensive deterioration index is put froward based on thee theory of fuzzy comprehensive analysis,and the corresponding criteria are set up also.The data processing system,being used to do the calculation of deterioration index and to make the wear extent judgement,is developed by the authors.Practical application showed that the introducing of deterioration index not only makes the ferrographic quantitative index become more perceptible but also makes the ferrographic quantitative indexes obtained from different monitored equipments become more comparable,so the introducing of deterioration index advances the develoment of ferrographic quantitative monitoring technique.