Based on the field survey of species composition and diversities in six typical plant communities of Songshan Nature Reserve, Beijing in 2017, we selected the diversity indices of α and β to describe the plant diversity characteristics of arborous, shrub and herbal layers and their main dominants. (1) The standard plots surveyed in Songshan Nature Reserve were composed of 75 species which belongs to 58 genera and 40 families. Major dominent species in arborous layer were Pinus tabulaeformis Carr., Quercus mongolica, Populus tomentosa Carr. and Populus davidiana. Spiraea pubescens Turcz. and Grewia biloba G Don were dominant or subdominant species in the shrub layer. Compositae species were widely distributed in herbal layer. (2) ShannonWiener and richness indices were sized as herbal, shrub and arborous layer. The indices of α diversity in herbal layer increased with elevation, of which layer the richness and evenness influenced α diversity significantly. (3) Considering the variation of β diversity along the altitudinal gradient, herbaceous common species decreased at first and then increased, while turnover rates of species were gradually increased first and then decreased. Therefore, the synthetic regulation of stand structure and microtopography should be considered on biodiversity conservation which followed the law of natural succession, formulating reasonable and feasible conservation experience and technology to provide scientific support for the protection of forest community diversity and its ecological function.