Abstract: At present, the research on understory grass in China mainly focuses on artificial forests, and there are few studies on natural forests. For the study of the distribution and species diversity of natural trees in Chongqing municipality, the Berger-Parkar index,Simpson index, Shannon index, Pielouand index the species composition and structure of natural arbor forest in Chongqing. The results show that:(1) The sedge of Sargasaceae and the awn and setaria of Graminae are widely distributed in the arbor forest.(2) BergerParkar index and Shannon index decrease with the increase of depression; the dominance index of the Simpson; the Pielou index shows no change significantly. In general, the composition of understory herbs in different canopy forests in Chongqing has obvious differences.