Agricultural areas are mainly distributed in the suburbs, however suburs of metropolis are often used as flood storage and detention areas in order to ensure the safety of urban from flood. Severe land subsidence would make a decrease use of flood control facilities like dike and sluice which protect the agricultural areas, and there are important significance to analyze the flood control in agricultural areas affected by double natural disasters. In this paper, the land subsidence observations and sedimentation rate over recent 20 years in Dahuangbao agricultural areas are the object of study, and the flood routing mathematical model is established using the alternating direction implicit method (ADI) with high stability and precision. The results reveal that after comparing the flood values with different return periods between before and after land subsidence, the inundated area and capacity after land subsidence increases, which directly affects the safety of agricultural areas.