According to the investigation on Pinus tabulaeformis forest in Zigui County, species diversity of the forest was studied. Result showed that the number of species in Pinus tabulaeformis forest increased 67.5% contrast to grassland, the primordial vegetation, and that species diversity became richer than grassland. The Shannon diversity index of the forest reached 3.0379. But because species in arborous layer was monotonous, its Shannon diversity index was less than nearby broad-leaf forest. Species diversity on various quadrats was related to the number of Pinus tabulaeformis and its growth, which depended on sowed density of seeds, slope direction, slope degree and so on. The relationship between species diversity and habitat was also discussed in this paper.