[Objective] The cultivated land use information was accurately extracted in order to provide theoretical support for farmland management and scientific use of cultivated lands. [Methods] Effective area of arable land in the Naoli River basin was determined using grey system theory and associated theoretical assumptions, mathematical models, mutation detection model, and empirical analysis. Data used in the study came from land use change survey data and the net cultivated land coefficient. [Results] Land use area showed significant grey characteristics. If accumulative treatments were applied to the area of the arable map within a certain area, the linear differential fitting equation could be used to predict the effective area of arable land in Naoli River basin. The grey system theory hypothesis could be applied for the accurate extraction of dryland and paddy fields. In 2018, the effective area of dryland and paddy fields was 1.06×10⁶ hm² and 3.87×10⁵ hm² in the Naoli River basin. The effective dryland coefficient and the paddy field coefficient were 97.65% and 98.07%, respectively. At the same time, the spatial distribution of effective arable land showed that more attention should be given to their actual utilization and development status in the downstream area of the outer Qixing River in the Naoli River basin, and in the northern part of Youyi County and the western part of Baoqing County. [Conclusion] Grey system theory was proposed for determining changes in effective area of arable land. Gray system theory was found to be feasible for extracting effective cultivated land and its coefficient.