Abstract: Statistical map is the kind of important forms of thematic map,and data classification is the kernel.In this paper,the quantificational indexes of classification evaluation are discussed,when changing the number of classes,the spatial data autocorrelation degree is changed,this law is researched.Based on this law,the number of classes can be determined,and this new method is given in this paper.The result of data classification should be further evaluated by means of spatial distribution characteristic of data,and an example is given to test it.