Based on the results of experiments on the regulation of water and fertilizers to spring wheat in farmland of semi-arid regions, the paper discusses optimum matching of water and fertilizers from the point of view of farmland ecology and studies the dynamic laws of leaf area, leaf area index and the value of leaf area duration of spring wheat with different amounts of water and fertilizers. It establishes the growth model of spring wheat and a statistical model between the integral of leaf area and the yield, and analyzes quantitatively the relationship between the coefficient of minimum water consumption and the optimum amount of fertilizer. The results are important for utilizing the limited precipitation resources and high efficient yield of spring wheat in semi-arid regions.