Niche is an important means to study the ability of plant population to utilize and adapt to natural resources. Using niche theory, we studied the community 10 shrub species and 11 herb species under Picea crassifolia and Betula platyphylla mixed forest of high hill regions in Datong County, Qinghai Province. Results indicated that: 1) Potentilla fruticosa and Salix cupularis in shrub layer had larger niche breadth, so did Polygonum viviparum and Fragaria orientalis in herb layer, which suggests that these vegetations were scattered widely under the mixed forest, with a strong adaptation at the present stage. 2) Two populations with a broad niche breadth had generally a large ecological niche overlap, while those with a narrow niche breadth had generally a small ecological niche overlap. Some populations with a narrow one also probably had a large ecological niche overlap. Apart from this, the niche overlap of species belonging to the same genera might be small, which is mainly associated with their evolution and succession. 3) In terms of eco-response rate, Spiraea salicifolia of the shrub layer and Galium boreale of the herb layer were more aggressive than other species, and Euonymus przwalskii of the shrub layer and Galium aparine of the herb layer declined in a rapidest rate. The results of our study could be a guidance and theoretical basis for the projects of converting cropland to forest and ecological forest afforestation in high hill regions of Datong County, Qinghai Province.