For improving the deficiency of evaluating factors that cause GIS fuzzy uncertainty, the paper evaluates GIS quality to use principle of multilevel fuzzy synthesis judgment of fuzzy mathematics. The conclusion manifests that the method of multilevel fuzzy synthesis judgment not only makes clear perfectly consider the effects of all factors and their actions each other on GIS quality, realizes reasonable and fixedly quantitative analysis on GIS quality, and provides a decision - making basis on improving GIS quality because it reflects key factor that affects GIS quality in a certain extent ,but also it is simple, practical and reasonable. 