Using the grass yield and spectral data observed in the years 1989-1991 in different types of natural grassland in the middle section of the Tianshan North Slope and the synchronous NOAA/AVHRR data, the correlation coefficients between the grass yield and various vegetation indices are calculated. The results show that there exists an obvious correlation between the grass yield and various vegetation indices. The dynamic monitoring spectral model of the grass yield is established. The correlation coefficient between the dry weight of grass and the NOAA/AVHRR ratio vegetation index is 0.7597, and that between the green weight of grass and the NOAA/AVHRR ratio vegetation index is 0.8066. Then the satellite remote sensing monitoring model of grass yield is established. This model can be used to monitor the grass yield of natural grassland.