The species diversity of five forest communities of the loess plateau in the north of Shaanxi province is measured with species diversity index(Shannon-Wienner index, Marg alef'index,Simpson's diversity index),evenness index and species richness.The result shows that the species diversity of Populus davidiana forests is the highest in five forest communities.The species diversity index and richness index for different strata is in the following order:herb stratum> shrub stratum> tree stratum.As for the evenness index,the order is tree stratum< herb stratum,tree stratum< shrub stratum while species diversity of herb stratum has no significant difference with shrub stratum.