To reveal the environmental regulation mechanisms of the formation of diversity and biomass of the shrub and herb in shrub communities of the dry-warm valley in the middle reaches of the Lancang River, the relationships of species diversity and biomass with environmental factors were analyzed through field investigation. The results show that a total of 42 shrub species belonging to 36 genera of 23 families and 96 herb species belonging to 76 genera of 34 families. Based on the importance values of the shrub dominant species, seven communities are identified. The importance value of the first shrub dominant species is the highest (0.710) in the Vitex negundo var. microphylla Hand.-Mazz. community, while the first herb dominant species include Eragrostis ferruginea (Thunb.) P. Beauv., Arthraxon prionodes (Steud.) Dandy, and Digitaria sanguinalis (Linn.) Scop. Among the shrub, the Shannon-Wiener diversity index, Margalef richness index, and species richness index of the Ceratostigma minus Stapf ex Prain and Caryopteris minor (C. Pei et S. L. Chen ex C. Y. Wu) C. L. Xiang communities are significantly (P<0.05) higher than those of the V. negundo var. microphylla, Elsholtzia capituligera C. Y. Wu, and Excoecaria acerifolia var. cuspidata (Müll. Arg.) Müll. Arg. communities, while their Simpson diversity index is only significantly higher than that of the E. capituligera community; no significant differences are observed in herb species diversity indices between communities. The shrub biomass of all seven communities is higher than the herb, among which, the shrub biomass of the V. negundo var. microphylla community is the highest (176.72 g·m^-2), and the herb biomass of the E. capituligera community is the highest (61.77 g·m^-2), but there are no significant differences in shrub and herb biomass between communities. Elevation and mean air temperature in July are the common dominant factors regulating the shrub and herb species diversity; the shrub species diversity is also affected by distance to water source, slope position, and cumulative precipitation in July, while the herb species diversity is also affected by slope aspect. The shrub biomass is mainly affected by slope, slope position, elevation, mean air temperature in July, cumulative precipitation in July, soil total nitrogen content, and soil organic matter content; the herb biomass is affected by slope position, elevation, mean air temperature in July, cumulative precipitation in July, and soil total nitrogen content. Overall, the shrub is more sensitive to environmental factors than the herb.