In lake ecosystems, the timing, duration, and frequency of inundation greatly determines the wetland/aquatic ecological conditions, and influence wetland plant regeneration and species richness. Under increasing impacts from human activities and climate change, a better understanding of how hydrological changes influence wetland vegetation is required. In this study, we analyze the spatial distribution of the inundation frequency and its temporal variation during the period from 2000 to 2015 in Poyang Lake by means of MODIS image interpretations method based on mixed pixel decomposition model derived from the spectrum characteristics of ground features. The relationship between the inundation frequency and the vegetation abundance is further discussed. The main results are as follows:(1) the spatial distribution of inundation frequency in the receding period shows a decreasing trend from north to south on the whole. Areas with high inundation frequency are distributed in patches. (2) The inundation frequency of the whole lake decreased from 2000 to 2010, then recovered to a relative stable state from 2011 to 2015. In different regions of the lake, the temporal changes of inundation frequency in the last 15 years shows different trends. The inundation frequency of the northern river channel and that of the central shoal shows trends similar to that of the whole lake, except that the changes of inundation frequency in the central shoal are gentler. On the other hand, the inundation frequency of the southern sub-lake is basically unchanged. (3) The vegetation abundance closely responds to the inundation frequency of Poyang Lake. The "n" form distribution on the scatter diagram of vegetation abundance versus inundation frequency shows that there were high values in the central part and low values on both sides, and the vegetation abundance reaches a maximum when the inundation frequency equals~40%. (4) The relationship between the inundation frequency and the vegetation abundance indicates a positive spatial evolution of emergent aquatic vegetation in Poyang Lake.