In this paper, an approach to assessing ecological suitability of crop growth was developed using GIS, through a case study of maize planting in Jilin Province, in the northeast China, in order to improve the accuracy and objectivity of the evaluation, promote the rationality of crop distribution, and increase the efficiency of the agro-resource utility. Climate and soil conditions in the region were taken into consideration in the research. The crop potential productivity under the climatic condition of 46 meteorological stations in the region, namely photo-temperature-water climatic potential productivity, was calculated based on the meteorological data of the precipitation, temperature, wind speed and sunshine hours from 1980 to 2006, and the crop potential productivity was used as index to evaluate the climatic suitability for crop growth. The point data were interpolated in a GIS environment and formed climatic suitability map. The assessment of soil suitability for crop growth was derived from soil fertility map drawing on the basis of information on 12 parameters, such as terrain, depth of soil body, thickness of black earth, soil erosion and organic mater. The ecological suitability map is completed using methods of spatial overlay in GIS. Comparing with the crop yield map that based on the statistical yield of 30 years in each county, the result of ecological suitability assessment is consistent with the yield. Therefore this method is feasible to assess the ecological suitability in the region.