Abstract: The rapid economic and social development has continuously reconstructed the spatial pattern of the built-up area expansion intensity since 1978 in the Yangtze River Delta. The research on its spatial characteristics and driving mechanism can provide support for the scientific, orderly and sustainable region development. The Yangtze River Delta is one of the regions with the most dynamic expansion of built-up area in China. This paper analyzed the spatial-temporal dynamic characteristics of the built-up area expansion intensity for 41 cities in the Yangtze River Delta using an impervious surface dataset from 1978 to 2017. And the geographically and temporally weighted regression (GRWR) model was applied to discuss the driving factor. The results showed that: (1) with the fast urbanization, the regional differences of the built-up area expansion intensity in the Yangtze River Delta has been constantly increased, and the spatial difference has also been obvious. The regions with high intensity have an alternate expansion. The expansion process has gradually appeared in the cities along the Yangtze River and the coastal areas of Zhejiang Province, which has led to a Z-shape spatial pattern. (2) The region including Shanghai, Nanjing, Hefei, Hangzhou, and Ningbo has a more drastic change process in the whole study area. This region has obvious agglomeration effect of core city and path-dependent characteristic. (3) The neighborhood relationship of the built-up area expansion intensity has strong spatial-temporal agglomeration and is dominated by positive collaborative increase. Most of the cities are in a relatively stable spatial state. (4) The factors such as population, economy, administration work together to change the urban built-up area expansion intensity, and the main driving factors are various in different periods. It shows the transformation from economic total quantity to economic quality, and from economic activity to government supply policy.