The integration of the Yangtze River Delta has become a national strategy. The natural, social and economic factors are closely related and the regional interaction is significant in the Yangtze River Delta. As the basic unit of the administrative division of the Yangtze River Delta, the sustainable development of the county plays an important role in the integration and coordinated development of the region. This study took the Changxing County in Zhejiang Province as an example. Combining the development potential with ecological constraints, a universal index system and evaluation method was constructed for the evaluation of territorial spatial development suitability. The spatial accessibility analysis method was used to evaluate the development potential, and the land of ecological constraint was evaluated based on the minimum cumulative resistance (MCR) model. The suitable land for development in Changxing was identified based on the potential-constraint model, which was 358 km² and covered 24.6% of the total area, mainly distributed as a middle-clustered and around-scattered pattern. Based on the results, some suggestions for the future development were put forward. In order to optimize the layout of territorial spatial development of Changxing in future and guide the territorial spatial plan in county scale, the county needs to establish and improve relevant systems to protect arable land, strengthen territorial space control to protect ecological space, carry out ecological restoration to ensure ecosystem health, and prevent natural disasters by various means.