During the past ten years, the land coverage has changed a lot in Northwest China. Using the Land Coverage Dynamic Monitoring System NOAACHAIN, the NOAAAVHRR image data of Northwest China in August 1990 and 1999 is pre-processed. In this article the detail processes of atmosphere correction and geo-correction, and the calculation of system parameters are described. Through the statistics of vegetation index NDVI, the change in land coverage is obtained between these two periods. The results showed that the ...