In this paper， herbaceous communities in the Loess Plateau were taken as research object， four vegetation belts from Yuyang， Yulin， Shaanxi to Fuxian， Yanan， Shaanxi were selected to measure species diversity and biomass of herbaceous communities， combined with the meteorological data of the last 20 years in the study area. The distribution characteristics of species diversity and biomass of herbaceous communities in the four vegetation belts and their response rules to precipitation changes were analyzed， so as to provide references for vegetation restoration and ecological construction of soil and water conservation in the Loess Plateau. The results showed that： (1) Margalef index， Pielou index and ShannonWiener index of herbaceous communities in the four vegetation belts were the smallest values in the grassdesert belt and the largest values in the forest belt. The values increased first and then decreased with the increase of annual average precipitation， and the maximum values all appeared in the forestgrass belt. (2) The order of aboveground， underground and total biomass is grassdesert belt< forest belt< grass belt< forestgrass belt. With the increase of annual average precipitation， they showed a trend of “single peak curve”， and the inflection points of the curves all appeared in forestgrass belt. There is a significantly positive correlation between underground/aboveground biomass and annual average precipitation.