Abstract: The utilization of water resources in the Sanjiang Plain depends largely on the agricultural structure, where most dry land crops have changed into rice since 2000. It is necessary to explore the balance of soil and water resources, thereby obtaining an optimal utilization scale of cultivated land for sustainable development in China. In this study, the Naoli River Basin was taken as the research area, which was an important commodity grain production base in China. Most datasets were related to water and soil resources, including the remote sensing information, meteorological station, and spatial distribution of cultivated lands. A balance model of soil and water in farmland was established according to the fundamental principle. An evaluation was made to clarify the allocation status of water and soil resources in Naoli River Basin. A quantitative investigation was carried out to obtain an optimal scale on cultivated land suitable for development and utilization, combined with crop irrigation data. The results showed that: 1) The current reclamation rate of Naoli River Basin was 62.61%, and its proportion of paddy field to cultivated land was 37.33%, which was in the middle stage of paddy fields. Evapotranspiration under water stress was the same for dry land and paddy field. The river basin also showed that the water deficit for paddy field was significantly higher than that for dry land; 2) The supply of irrigation water in Naoli River Basin was from 21.23 to 211.91 mm, where the demand for irrigation water in paddy field was higher than that in dry land. Water resources in Fujin City, Youyi and Jixian County were in the overload state, where there were more land resources and fewer water resources for the paddy fields. The current water resources supply conditions cannot meet the demand of cultivated land water; 3) Besides, water resources in Qitaihe City, Shuangyashan City, Raohe and Baoqing County were in the overload state, showing the obvious characteristics of fewer land resources and more water resources. A suggestion can be that the expandable paddy field area of Naoli River Basin cannot exceed 1 101.80 km2 in the future, where the proportion of paddy field to cultivated land was controlled below 44.76%. The scale of the paddy fields can be appropriately reduced in Fujin City, Youyi and Jixian County. In Baoqing County, the key dry land can be converted into paddy fields. The findings can be used as a sound references for the cultivated land management in the Naoli River Basin and the Sanjiang Plain.