Nowadays leanness implementation was more and more widely applied in production organizations to eliminate various kind of waste and reduce overall cost of business firms. During the implementation process, the incorrect choices of implementation areas may result in high cost but no obvious improvement, even the appearance of employee dissatisfaction. In this study, a leanness assessment method based on principal criteria searching approach was established. Principal Component Analysis was used to assess and improve lean performance throughout the entire organization, qualitative factors were considered as well as quantitative factors based on fuzzy logic. Throughout the identification of key leanness factors of an specific industry, a comprehensive assessment model corresponding to the characteristics of that industry was established. Finally a case study of a Chinese special purpose vehicle manufacturing organization was presented, the results show that the correlation among 15 different leanness factors and 8 principal indicators mainly contributed to the leanness performance, thus the overall measurement of leanness performance of several workshops could be achieved.