The paper combines project cost estimating field features,enhance the ability of managing tacit knowledge and increase the organizing level and applying benefit of case.The technical thought and system working process of case-based reasoning ( CBR ), are introduced and analyzed in detail firstly in this paper, and discuss the introduction of CBR in the engineering field knowledge management on this basis. Meanwhile,integrate specific engineering practice case--XX Roads Comprehensive Renovation Project, do further research on the engineering cost estimation system of knowledge management applications based on case technology, and achieve knowledge reuse and innovation, as well as the shared values of knowledge resources.