Abstract: Based on the theory of equipment deterioration， this study analyzes the deterioration process of the bottom assembly. The results show that material attrition is the main inducement of bottom assembly wearing. As the time elapses， its failure rate is increasing nonlinearly， and the inferior value is distributed in the form of exponential function. According to the actual survey data of the overhaul and maintenance costs of fifteen major locks′ bottom assembly attached to Waterway Management Bureau of Grand Canal in North Jiangsu Province (WMBGCNJP)， the original value， inferior value and annual running cost of bottom assembly are determined. The economic life of the locks′ bottom assembly is determined to be 13~15 years by using the static model and dynamic model having the inferior value method. Comparing with the wear loss of the bottom assembly in an overhaul period， this method is reliable and has reference value for decision making of bottom assembly replacement and determination of the cycle of lock overhaul.