The study on land use is one of the important content in global change research, and is also of the hot site in the geographical study. Taking rationality of land use of YULIN as the research object, this paper focuses on the method to classify rationality in the view of fuzzy pattern recognition theory. During the analysis, firstly, authors establish classification indexes system by choosing eight factors (cultivated land, woodland, meadow, etc) as the evaluate indexes, and then classification grade criterion determined by classifying eight factors into six grades. Moreover, values of 5,4,3,2,1 are evaluated to the eight indexes of classification grade criterion respectively. In order to evaluate rationality of land use, functions that determine the rationality subjection of fuzzy grade are established on the basis of gray system theory in this paper. In order to insure the oneness of each index of classification indexes system, the authors have transformed original data, and the ratio of land use is got from original data of each county’s land use of YULING. By using the function established in this paper, fuzzy grades matrix of each classification index are calculated, and rationality grade of land use of each county’s in YULIN is made out by using fuzzy synthetical measurement method. According to the calculation and analyses, rationality grades is made out respectively as following: YULIN, SHENMU, SHUIDE belongs to the grade of 5; HENGSHAN belongs to the grade of 4; FUGU, MIZHI, JIAXIAN, WUBAO, QINGJIAN, ZIZHOU belongs to the grade of 3; JINBIA belongs to the grade of 2; DINGBIAN belongs to the grade of 1, which is close to the fact of land use of YULIN area. This study shows: fuzzy synthetical measurement is a scientific and practical method to be used to classify the grade of land use rationality, which takes on characters of complexity, random city, uncertainty and other non line features.