In this paper, taking vegetation of karst area as the research site, MODIS NDVI, MODIS EVI and climatic information of 2001 to 2010 are used to analyze the relationship between vegetation and climate changes. Vapor pressure, precipitation, relative humidity, maximum temperature, minimum temperature, mean temperature, dew point, air pressure, wind speed and sunshine hours are taken as climatic variables to explore the relationship between vegetation index and climatic factors over different stages. Then, differences between NDVI and EVI in response to climate factors of karst area are analyzed. The objective is to provide references for reasonable use of vegetation index to monitor vegetation changes. The results show that: 1) There is a significant correlation between vegetation index and most climatic factors for both EVI and NDVI in karst area, yet differences between NDVI and EVI responsing to climatic factors are obvious. The correlation between EVI and climatic factors are obviously higher than that of NDVI except for sunshine hours. The correlation coefficients between NDVI and climatic factors are much higher for sunshine hours, maximum temperature, and mean temperature, their average values of correlation coefficients are 0.616, 0.535 and 0.474 respectively. While the correlation coefficients between EVI and climatic factors are much higher for vapor pressure, mean temperature and dew point, their average values of correlation coefficients are 0.857, 0.844 and 0.839 respectively. 2) There is a significant lag in the response of EVI to most climatic factors. Compared with EVI, lag is stronger for NDVI than that of EVI. The highest correlation coefficient between EVI and most climatic factors appear at the earlier stage of -1, while the highest correlation coefficient between EVI and most climatic factors appear at the earlier stage of -2. For sunshine hours and wind speed, no response lag of two vegetation indices exists. The response of two vegetation indices to climatic factors is consistent for all stations except for relative humidity, sunshine hours and wind speed.