Abstract: Urban agglomerations have become important growth poles and core areas for economic development in western China, and a reasonable and orderly spatial structure is an important source of economic growth. The paper is based on panel data of eight urban agglomerations in western China from 2004 to 2020, and uses the dynamic spatial Dubin model to test the effect and mechanism of the spatial structure adjustment on economic growth in the western urban agglomerations. The research results show that the spatial structure adjustment of population, industry, and land use in urban agglomerations in western China mainly manifests as spatial agglomeration and significantly promotes economic growth; further examination reveals that the promoting effect of these three types of spatial structure agglomeration on economic growth is constantly increasing, and it has evolved from short-term promotion to coexistence of short-term and long-term promotion. In terms of impact mechanism, the population spatial agglomeration of urban agglomerations in western China has suppressed economic growth due to intensified environmental pollution, but the inhibitory effect is significantly weaker than the positive promoting effect; industrial spatial agglomeration supports economic growth by fostering technological progress; The spatial agglomeration of land use promotes economic growth by accelerating the upgrading of industrial structure. Finally, the paper proposes policy recommendations to enhance the population carrying capacity of central cities in urban agglomerations, the spatial agglomeration of the secondary and tertiary industries within urban agglomerations, and the spatial agglomeration of construction land.