Mountainous areas are characterized by high biological diversity but are threatened by agricultural reclamation. To evaluate the effects of agricultural land use and woody crop intercropping on carabid diversity in mountainous regions, we compared the diversity of carabid beetles and their body size compositions in two walnut plantations (monoculture and newly established intercropping system) and two secondary succession habitats (secondary forest and grassland) in 2011 and 2012. Carabid activity-abundance did not differ among the walnut plantations and secondary succession habitats for both sampling years, and species richness was higher in the walnut monoculture in 2012. However, the secondary succession habitats harbored more large carabid individuals than the walnut plantations. All of the carabid species compositions in the walnut plantations differed from those in the secondary succession habitats, whereas the species compositions of large carabids in the walnut plantations differed from those in the secondary succession habitats in 2012 but were similar in 2011.We conclude that converting secondary succession lands to walnut plantations had little effect on both the alpha diversity and species turnover of carabid assemblages, but the secondary succession lands were essential for sustaining diverse large carabids, which comprised conserved species and natural control agents. The newly introduced walnut-chrysanthemum intercropping system did not produce significant short-term losses in carabid diversity compared with the walnut monoculture system, but the concept that the walnut-chrysanthemum intercropping system could serve as a trade-off between production and biodiversity conservation will require long-term monitoring.