Understory herb diversity is an important indicator to measure the structure and function of forest communities. In this study, pure forest of Cunninghamia lanceolata plantations (I), mixed forest with C. lanceolate and Sassafras tzumu plantations (Ⅱ), and mixed forest with C. lanceolate, S. tzumu and Betula luminifera plantations (Ⅲ)), these three different types of Cunninghamia lanceolata plantations in Jiuhua Mountain Forest Farm, which located in the west of Hubei Province, were selected as the research object. By analyzing the understory herbs layer species composition and its diversity characteristics, we explored the relationship between forest types and understory herb diversity. Results showed that totally 72 species of plants in the herb layer were found in this study area, belonging to 65 genera of 37 families, of which the Rosaceae, Thelypteridaceae, Gramineae, and Compositae were the majority. Research indicated that the understory herbaceous species were dominated by perennials, with 67 species in total, accounting for 93.06% of all species. The species richness index, Shannon index, and Pielou uniformity index were higher in the mixed forests (Ⅱ and Ⅲ) than those in pure forests (I). However, the difference was not significant. Meanwhile, we found that the elite species of herb layer were closely related to the tree species composition of the woodland. Among them, the type I forest was dominated by Rubus lambertianu, Parathelypteris glanduligera, and Houttuynia cordata, and their important values were 13.65%, 8.79%, and 5.27%, respectively. Type Ⅱ and type Ⅲ plots were dominated by P. glanduligera, Arthraxon hispidus, and Kalimeris lautureana, with important values of 10.75%, 8.37%, 7.47% and 11.84%, 6.16%, 5.82%, respectively. In addition, the dominant species of the herb layer can significantly affect soil properties. For example, P. glanduligera was significantly positive with soil moisture content (P<0.05) and R. lambertianu had a significant positive correlation with soil phosphorus content (P<0.05), while Opiopogon japonicus was negatively correlated with soil phosphorus content (P<0.05). Moreover, a certain synergy and competitive relationship was found among the elite species in the herb layer.