Based on the analysis of the past 30 years climate change characteristics in Yangtze estuary area, the normalized difference vegetation index (NDVI) of the Chongming Dongtan Wetland in Yangtze River Delta was calculated on the basis of 107 TM and ETM~+ images, which were collected by the Landsat satellites. The wetland vegetation activities were shown by the index. By studying their characteristics of seasonal vegetation activity during 1984-2013, the control factors of intra-annual and inter-annual vegetation activity were revealed. Moreover, this study showed the wetland vegetation's response characteristics to climate changes. The results can be summarized as follows. (1) Climate variation in Yangtze River Delta was that the temperature increased and sunshine duration decreased significantly, while there was no significant variation of the precipitation. The temperature increased significantly in different seasons (except winter), while the tendency of precipitation and sunshine duration was not significant. (2) The seasonal variation characteristics of wetland vegetation were identical in the last 30 years. NDVI increased with time, but its velocity and significance varied. NDVI growth rates in winter and spring were larger, with 0.07·10a~(-1) and 0.06·10a~(-1); growth rate in summer was slightly lower with 0.04·10a~(-1); the tendency in fall was not significant. (3) The NDVI of wetland vegetation showed a single-peaked variation characteristic in term of seasonal variation in one year. They increased in spring and reached the maximum (NDVI_(max)=0.63) in midsummer (the 188~(th) day and 189~(th) day in the year), then the value began to decrease and reach the lowest value in winter. Seasonal variation characteristics of the vegetation NDVI were mainly controlled by monthly mean temperature (R~2 = 0.84).