Spatial data mining is to extract the unknown knowledge from a large-amount of existing spatial data repositories areas. The spatial data are to represent the spatial existence of an object in the infinitely complex world. Although uncertainties exist in spatial data mining, they have not been paid much attention to. If the uncertainties are made appropriate use of, then it may be able to avoid the mistaken knowledge discovered from the mistaken spatial data. The uncertainty parameters (i.e. supportable level, interesting level and confidence level) may further decrease the complexity of spatial data mining.