This paper focuses on the elevation variation of urban and rural construction land expansion. It uses 1985, 1995, 2000 and 2010's land use data and 90 m resolution DEM data, and establishes evaluation indexes including density index, incremental proportion, sprawl rate, sprawl intensity index and evaluation index of construction land, to explore the characteristics of spatial heterogeneity and the evolution pattern of urban and rural construction land elevation changes in Taihu Lake Basin. The research results indicate that: the hotspot of construction land expansion has transferred from medium-elevated region to higher-elevated and lower-elevated region in the whole basin, of which the former trend is more significant. Spatially, construction lands distributing along the plain river network in the eastern downstream watershed, in the city and town concentrated areas along the Yangtze River in the north, and in the valley areas of upper reaches of Tiaoxi stream have the trend to expand to lower-elevated region. However, except for Tiaoxi stream basin, the other hill regions in the upstream basin are expanding gradually to higher-elevated zones. The development of new districts and cities has promoted a rapid expansion of urban and rural construction land. Contradiction between the limited supplies of suitable land for construction and the huge demand of land driven by land finance has forced the construction land to expand to higher and lower elevation areas, especially to lower areas in city and town concentrated areas in southern Jiangsu Province. Construction land expanding to lower altitude regions will inevitably occupy the natural water storage space, divide and obstruct the natural flood discharge channel, and lead to difficulties for flood to be discharged in the low-lying place. While construction land expanding to higher altitude regions will accelerate the confluence water and shorten the downstream flood peak time, which lead to regional hydrological security risks and frequent waterlogging disasters.