The normalized difference vegetation indexes (NDVI) of the wetland in Lake Nansi are calculated on the basis of MSS, TM and ETM + remote sensing data collected by the Landsat satellites. The activities of the wetland vegetations are deduced by these indexes. By studying the characteristics of seasonal vegetation activities of the wetland during 1973-2011, we revealed the control factors of intra-annual and inter-annual vegetation activities. Moreover, our study showed the response characteristics of wetland vegetation to climate changes, human activities and extreme drought events. The results can be summarized as follows:(1) The characteristics of the seasonal variation of wetland vegetation in Lake Nansi are not identical in the past 40 years. The NDVI in spring decreased first and then increased, which may be caused by the climate variation (temperature increase) and human activities such as reclamation and aquaculture in the study area; The NDVI in summer and winter present a significant decreasing trend due to the effects of human activities. However, the variation of the NDVI in autumn is comparatively small. (2) The NDVI and area of wetland vegetation all present single-peaked variation characteristics in term of seasonal variations in one year. They increase in spring and reach the maximum in late summer (the 202nd day and 205th day in the year), then decrease and reach the lowest values in winter. (3) To certain degree, drought is not the limiting factor for NDVI increase. In fact, since drought results in the drawdown of water level of the lake, the beach and lake bottom are exposed. All these factors probably increase the NDVI by prompting the growth of vegetation and enlarging vegetation area in the wetland.