With the rapid advancement of urbanization, population redistribution has become one of the factors affecting the human-land relationship and the restoration of vegetation and ecological improvement in mountainous areas of China. Using population distribution data, river system data, and MODIS data, this paper systematically analyzed the spatial changes in population and vegetation greenness along the different grades of the river in the mountainous areas in southwest China from 2000 to 2010. Then, the relationship between population spatial redistribution and vegetation change was quantitatively analyzed. The results showed that:(1) Population density along the rivers of Grade 3 and above had a higher increase rate in the affected areas compared with the comparison areas. The increase rates of population density in the affected areas were 75.9% and 42.1% higher than those of the comparison areas, along the primary and secondary rivers, respectively. (2) The EVI (Enhanced Vegetation Index) increased in both the affected and the comparison areas along the rivers of Grade 3 and above. The increase of EVI in the comparison areas were higher than those in the affected areas. (3) The trend of EVI variation had a negative relationship with the changes in population density, indicating that the increase in population density along the rivers influenced the improvement of the vegetation cover. For the rivers with higher grade, the correlation between population density change and the trend in EVI variation was stronger.