To analyze the effect of field input on grain yield and economic benefit of farmlands, we used wheat-corn double crop-ping fields in northern Taihang Mountain Plain region of central Hebei to analyze the degree of response to input from farmland quality on basis of factor combination, hypothesis testing, regression analysis and agricultural land grade. The results suggest that grain yield can be improved by scientifically and reasonably increasing field input or using a combination of factors at low input. High yield on farmlands with poor natural conditions can be achieved through scientific and reasonable input. The optimal value of field input is within the interval between the maximum input-output benefit and maximum grain yield. Reasonably adjusted input based on differences in the influence of natural factors on grain yield and different factor combinations can increase yield significantly.