The Great Wall is an example of linear cultural Heritage (LCH) subjected to a fragile ecological environment and unbalanced economic development. However, no studies have been conducted to assess the sustainable development suitability (SDS) of the Great Wall region. Heritage area development assessments can increase public and government knowledge of the state of heritage areas and aid decision makers in formulating sensible policies or plans to protect and develop heritage areas. The valley is the spatial model of mountain economic development proposed on the basis of a basin combined with the ecological protection, rural development, and cultural inheritance present in mountainous areas. This study chose 169 valley units in the Beijing Great Wall Cultural Belt as research objects. A 15-indicator assessment index system was established based on the ecological, socio-economic, and cultural dimensions. The assessment procedure was enhanced by employing the triangle graphical method, and spatial autocorrelation was used to study the geographical distribution features of the development suitability scores derived from the research region. The results show the following facts: (1) Yanqing, Huairou, Miyun, Pinggu, and Changping have high development suitability results, whereas Mentougou and Changping have low scores. (2) In total, 96 valley units have practical advantages, and 51.5% are comprehensive development types (with advantages in at least two aspects). (3) Valley development suitability scores spatially cluster into seven high- and low-value groups. The ecological carrying capacity of the Badaling Cluster cannot maintain its overheated development. The results match up well with the objective condition of planning in the Beijing Great Wall National Cultural Park. We conclude that the proposed indicator framework and analytical method can be transferred to cases with similar contexts.