Abstract: Using NOAA/AVHRR data observed at Urumqi, Fukang, Altai,Balikun monitoring station during 1992～1994, the annual variation characterisitics was studied and the differences of grass yield and AVHRR vegetation indices were compared. The grass yield and AVHRR vegetation indices had annual variation characteristics that their values were low in spring and then increaseed, the maximum values reached in summer and then they decreaseed. The AVHRR vegetation indices can reflect the changes of grass yield of different types of natural grasslands, therefore it is possible to classify different types of natural grasslands and to determine the optimum period of interpretation through AVHRR vegetation indices. The AVHRR vegetation indices can be used to monitor the grass yield and to predict the maximum yield because the AVHRR vegetation indices vary with grass yield in different seasons and from year to year.