Abstract: Taking the Xilinguole typical steppe as experimental area of the observation, the spectral reflectance, above ground biomass of grassland in different water treatments were measured and analyzed from May 2008 to May 2009. The results showed that amply irrigation improved grassland population and plant structure significantly, and increased the biomass of forage grasses. During vigorous growth period (July), grassland under enough irrigation had significant advantage in spectral reflectance characteristics, and in the four vegetation indices. During dead ripe period, there were significant differences（P＜0.05）among RVI (Ratio Vegetation Index) of grassland in different water treatment. During turning green period, there were significant differences（P＜0.05）among DVI (Difference Vegetation Index) of grassland in different water treatment.

Key words: Typical steppe, Spectral reflectance characteristics, Water fluctuation, Spectral reflectance, Vegetation index, Vegetation structure