Analyzing the ecological effects of construction land expansion supports optimized territorial spatial management and ecological conservation. Using multidimensional indices, ecosystem service value (ESV) assessment, and comprehensive evaluation methods, this study quantitatively examines the spatiotemporal characteristics and ecological effects of construction land expansion in the Yangtze River Economic Belt (YREB) from 2000 to 2020. Results indicate: ① construction land expanded markedly, increasing by 91.55%, with nearly 90% originating from cropland conversion, forming a high-density development corridor along the river centered on major urban agglomerations; ② the comprehensive expansion level increased in the west and central regions but remained spatially unbalanced, with higher intensity in the east due to development suitability and the siphoning effect of the eastern region; ③ expansion caused significant ecological impacts, including direct loss of ecological land and ESV, and indirect increases in human footprint pressure and carbon emissions; ④ a two-dimensional "expansion-ecology" classification identified four dominant types: medium-pressure balanced, low-pressure stable, high-pressure degrading, and low-pressure sensitive. These findings underscore the need for a coordinated mechanism to balance development and ecological protection, optimize spatial planning, and harmonize ecological security with high-quality development in the YREB.