Exploring the spatial extent of urban development within acounty is helpful to clarify the spatial relationships between urban land, permanent farmland, and ecological land, which lays an important foundation for the urban sustainable development of a county. Currently, the urban growth boundaries, and the existing permanent farmland and ecological protection boundaries have great conflicts with each other in different maps. Based on the new territory land spatial planning system, it is necessary to realize the "Three-Line Coordination" during territory land planning. However, the existing models of the delimitation of UGBs are highly subjective. The determination of the weight of each factor is usually subject to artificial influence, or only considers the dominant land use type without considering the other land use types. Thus, the simulation results of small-scale land use changes greatly differ from the actual results in the surrounding area. In this paper, we presented a delimitation method of urban development boundary based on the "Three-Line Coordination" and FLUS-UGB.We selected the Feng County in Jiangsu, China, as the study area where agriculture was the main development direction. Under the scenario of permanent farmland protection and ecological control, we delimited the urban development boundaries of Feng County. Our results show that: (1) the overall accuracy of the model was 94.7%, and the kappa coefficient was 0.895, which demonstrated the high simulation accuracy of our method; (2) under the baseline scenario, the spatial pattern of urban area presented a expansion trend. Under the scenario of cultivated land protection and ecological control, the urban area expanded outwards radially outside the permanent farmland and ecological control areas with an orderly manner; (3) the predicted area of urban development in Feng County would increase to 80.29 km² in 2035 with the growth rate of 69.07%. The boundary results predicted in our study can be used to effectively avoid the occupation of permanent farmland and important ecological land regions by urban development, leading toa better spatial coordination between urban expansion, and existing permanent farmland and ecological land protection in future. Moreover, our delimitation method of the urban growth boundary simulation was based on the "Three-Line Coordination", which met the demand of permanent farmland and ecological landprotection, and thus can reflect the urban land expansion of Feng County more accurately.