In order to realize the sustainable development of economy, society, and environment, the optimization of industry structure is the important aspect, and the choice of major industry is the key link. First, the selected indices for ecological agricultural county are determined. Second, the structure of index system and the weights of both criterion and indices are determined by means of principal component analysis. Then, the rank of its major industry capacity is got. Finally, its major industries are chosen. The actual examples show that the important references for major industry selection, development mode and growth way of ecological agricultural county can all be offered using the method proposed in here. . 8 Refs In Chinese