Abstract: The validity index of the result produced by fuzzy clustering based on two aspects is studied, which are the uncertainty of classification during fuzzy partition and spatial location feature of spatial data, and a new validity function of fuzzy clustering for spatial data is proposed. The experimental result indicates that the new validity index can accurately measure the validity of the result of fuzzy clustering. Specially, for the result of fuzzy clustering of spatial data, it is robust and its classification result is more perfect compared with other indices.