Biocrusts occupy wide and diverse ecological niches in arid and semi-arid climate regions, and thus they would dramatically affect the distribution pattern of herbaceous plants. However, the extent and pathways of their influences on the diversity and biomass of herbaceous plants are still in controversial. In a semiarid climate area on the Chinese Loess Plateau, we selected representative plots of uncrusted soil and cyanobacteria- and moss-dominated biocrusts, both on aeolian sand and loess soil, respectively. Then, the diversity of herbaceous plant community in each plot was investigated, and the total biomass was harvested and measured in laboratory. Based on the differences between the biocrusts and bare soil plots, the effects of biocrusts on herbaceous plant diversity and biomass were assessed, and the pathways of these influences were also analyzed using the gray relation analysis and structural equation model. Our results showed that (1) on aeolian sand, Gramineae and Compositae are the dominant herbaceous families in uncrusted plots, Chenopodiaceae is the dominant herbaceous family in cyanobacteria-dominated biocrusts plots, and Gramineae and Compositae are the dominant herbaceous families in moss-dominated biocrusts plots. Correspondingly, on the loess soil, uncrusted plots are dominanted by Compositae, Gramineae, and Leguminosae, which is the same as cyanobacteria-dominated biocrusts plots, and moss-dominated biocrusts plots are dominanted by Gramineae and Compositae. (2) As compared with the uncrusted soil, the cyanobacteria and moss-dominated biocrusts on aeolian sand increased the number of annual herbaceous species by 30% and 16%, respectively, and the number of perennial herbaceous species was increased by 44% by the cyanobacteria biocrusts but decreased by 46% by the moss biocrusts on the loess soil. (3) In comparison to the uncrusted soil, the cyanobacteria biocrusts on aeolian sand reduced the Patrick and Shannon diversity indices of herbaceous plants by 1.0 and 0.2, respectively, while the moss biocrusts on aeolian sand reduced these diversity indices by 3.4 and 0.5, respectively. On loess soil, the two diversity indices of herbaceous plants were decreased by 4.8 and 0.2, respectively, by the cyanobacteria biocrusts, while they were decreased by 4.2 and 0.4, respectively, by the moss biocrusts. (4) In comparison to the uncrusted soil, the total biomass of herbaceous plants in the cyanobacteria and moss biocrusts plots was reduced by 111.5 and 145.0 g/m², respectively, on aeolian sand, while that on loess soil was reduced by 127.8 and 172.2 g/m² respectively. (5) Soil penetration resistance had the greatest effect on herbaceous plant diversity with a correlation coefficient of 0.960 and 0.996 for aeolian sand and loess soil, respectively; while the contents of NH₄⁺-N and NO₃^--N had the greatest effect on herbaceous plant biomass with a correlation coefficient of 0.727 and 0.752 for aeolian sand and loess soil, respectively. In conclusion, biocrusts significantly reduce herbaceous plants diversity by increasing soil penetration resistance and thus reducing seed germination and limiting root extension, and they also reduce herbaceous plants biomass by hindering nitrogen adsorption from soil and thus limiting plant growth.