Geomorphic space serves as the foundational base and connective framework for surface features, playing a crucial role in urban construction. This paper takes the area within the outer city walls of Chang’an city in Han and Tang Dynasties as the research object, analyzing the spatiotemporal correlations between geomorphic space and urban construction. While existing research on Chang’an city in Han and Tang Dynasties is abundant, including discussions on the relationship between meso-scale structural morphology and geomorphic space, few studies have systematically explored the causal relationships between Geomorphic space and the entire urban planning process, such as site selection, orientation-axis establishment, outer wall formation, and spatial design, etc., or conducted comparative analyses of differential utilization of Geomorphic space between the two capitals. Employing comparative analysis and mutual verification of historical documents with archaeological remains, this paper investigates the area within the outer walls of Chang'an city in Han and Tang dynasties. From entire urban planning process perspective, it examines their connections with Longshou Plateau and surrounding mountains and rivers, aiming to reveal their distinct construction characteristics more profoundly and visually. The geomorphic spatial pattern of the Guanzhong district is centered on the Weihe River, with five major landform types-mountains, loess plateaus, plains, wetlands, and riverbeds-forming a multi-layered, stepped zigzag nested structure that exhibits asymmetric symmetry along the north-south axis. Early inhabitants established symbolic systems for prominent mountain features, and carried on the humanistic interpretation and utilization; The loess plateaus exhibited secondary erosion features of alternating plateau and lowland, and the groundwater is buried deep at the head of tableland but shallow at the end of tableland. The plains showed shallow groundwater tables, poor drainage, and eastern saline-sand areas. In capital site selection, Han and Tang Chang’an cities both recognized that locating at transitional zones between broad and flat plains and plateaus achieved optimal water accessibility-avoidance balance. Through analyzing water resources and terrain flatness of above geomorphic transition areas in Guanzhong district, the capitals were finally established in transition area of generalized Longshou Plateau and northern plain, and respectively established on the north and south sides of narrow Longshou Plateau. In orientation-axis determination, Han and Tang Chang’an cities were influenced by previous dynasties’ architectural traditions, its orientation experienced the shift from east to south, and successively established the mixed east-south axes, southoriented central axis. But all the axes took natural markers as their landing points, and all fell on the southern mountain peaks and valleys. These choices demonstrated precise correlations with geomorphic prominence, ridge-valley structures, and visibility.In outer wall morphology, although the landform of the two cities is not very smooth, they choose completely different construction methods due to the difference of the mainstream concept during the construction of capital cities in different dynasties. Han Chang’an city adopted irregular walls adapting to local conditions, whereas Tang Chang’an’s strictly rectangular walls reflected Confucian ritual constraints. In spatial design, both capitals skillfully utilized the geomorphic spatial pattern and morphological differences. Under the background of relative disorder and regular square,the hierarchical and three-dimensional image of the capitals were created in the layout of functional areas, building scale, height and structure.The study reveals that both capitals were guided and constrained by geomorphic space, exhibiting both homogeneous and differentiated utilization strategies. The conclusion of the corresponding relationship between geomorphic spatial characteristics and urban construction strategies provides case support for summarizing ancient urban planning patterns, offers deeper perspectives for heritage preservation and new city construction, and contributes to urban cultural continuity and sustainable development.