Abstract: Based on the daily temperature data of 31 weather observation stations from 1961 to 2010 in the Yangtze river delta, authors analyzed the variation characteristics of season length and starting date by using the trend analysis method, Mann-Kendall test method, and then analyzed the temporal and spatial distribution characteristics of seasonal climate variation by using the isoline technology. The temporal distribution results showed that the length of summer had a significant increasing trend（P<0.01）, and the starting time of spring and summer had a significant advancing trend（P<0.01 and P<0.05）during past 50 years in this study area. The spatial distribution results showed that the length of spring and autumn increased from inland to coast, the length of summer became longer from north to south and the length of winter became shorter from north to south. The spatial distribution showed that spring and summer became predominantly longer as while as autumn and winter became predominantly shorter, and the summer length changed most significantly（P<0.01）;the spring and summer started earlier in the south, while autumn and winter started earlier in the north; and the starting dates of autumn and winter had a delaying trend while spring and summer had an advancing trend at many stations.

Key words: Climatology, Season, Mann-Kendall test, Contour, Yangtze river delta