Abstract: Based on daily air temperature data at 112 meteorological stations in Yangtze River Delta and the change of construction land area within 10 km of each station from 1981 to 2015, the variation characteristics in the starting date and the length of four seasons (spring, summer, autumn and winter) and their impacts by urbanization were analyzed using climatic statistical methods, such as linear trend, Mann-Kendall test, correlation and significance test. The results showed that in the past 57 years, the starting dates of spring and summer in Yangtze River Delta were significantly earlier at 2.1 days and 1.7 days per decade respectively, while the those of autumn and winter presented a later trend by 2.0 days and 1.3 days per decade respectively, and showed earlier (later) trends in almost all regions. As a whole, the length of summer increased significantly by 3.6 days per decade, while that of winter shortened significantly by 3.5 days per decade in most areas of Yangtze River Delta. The length of spring and autumn did not change significantly. The starting date of four seasons all had abrupt change in the middle and late 1990s. There is a good correspondence between the increase of urban construction land area and the change of four seasons. The increase of construction land area caused by urbanization led to the change of surface physical properties, which changed the surface energy budget, promoted the seasonal temperature increase, and made the earlier spring and summer, later autumn and winter and longer summer and shorter winter.