Abstract: The fuzzy decision system for ecological distribution of citrus in north-cultivated-marginal area was established by using the data of mean extreme low temperature, accumulated active temperature (≥12.5℃), mean temperature in coldest month, annual mean temperature integrated with annual precipitation, days with mean extreme low temperature below -9℃,physiognomy, elevation, inland water body, cold air barrier, and soil nutrition and pH value. The complex reasoning model with imprecision was used in the decision system by introduction of L-R fuzzy number and recognition formula, which made the decision system have a wide range of application in practice. An example of applying the decision system was tested in Anhui province. The result showed that the development of the decision system would provide a useful tool for the decision of the ecological distribution of citrus in north-cultivated-marginal area.