Abstract: Irrigation water sources can greatly contribute to the reserve resources of arable land in northern China. National water network projects have also promoted the arable land reserve resources in recent years. In this study, a systematic evaluation was performed on the potential of cultivated land reserve resources under a water supply project in the northern region. The constraints of natural suitability, efficient use, and stable development were comprehensively analyzed to consider the ecological and spatial fragmentation of arable land reserve resources. The three-dimensional magic square was adopted to select evaluation units. Finally, the arable land reserve resources were optimized to fully meet the three requirements of sustainable ecology, natural quantity, and efficient quality. The results show that: (1) In rain-fed agriculture scenario, the area of unsuitable (Level I) development for cultivated land reserve resources in the unused land in the north was accounted for as high as 96 %, about 1.036 million km², and the areas of barely suitable (Level II), moderate (Level III) and high (Level IV) were 2.9×10⁴, 1.0×10⁴ and 6.0×10³ km², respectively. Thus, the unused land shared less potential space to meet the reserve development of cultivated land under the limitation of natural precipitation. (2) In the irrigated agriculture scenario, the potential of arable land reserve resources increased significantly in the north region. The area suitable for arable land reserve resources increased to about 2.0×10⁵ km², accounting for 18% of the total area, mainly located at the edge of the Junggar Basin in Xinjiang, the edge of the Tarim River, the Shule River Basin in Gansu, and part of Inner Mongolia. (3) A comparison was made between the rain-fed and irrigated agriculture scenarios. Irrigation conditions with relatively scarce water resources were required to greatly improve the arable suitability of land resources at the naturally appropriate level. The suitable cultivated area increased from less than 3 000 km² under the rain-fed scenario to about 48 000 km², in order to optimize the allocation of land resources. (4) There was a small error in the geographical location and the number of cultivated land reserve resources, compared with the previous. Therefore, the evaluation model of cultivated land reserve resources presented high accuracy and credibility. The findings can provide a strong reference for the development and utilization of arable land reserve resources under the national water network projects in China.