Community structure and their responses to environmental changes have long been a major concern in ecology. Constructed by body size and abundance, size spectra correlate with trophic transfer efficiency, respond process rate dynamics, and characterize ecological stability. Thus, body size spectra (BSS) can be an indicator of functional diversity to predict and characterize how community composition and ecosystem function respond to environmental pressures. The initial focus of BSS was in aquatic ecosystems until recently, when it was used in the community ecology of soil invertebrates. The present study briefly reviewed the concept, background, and theoretical basis of BSS. Four different but often confused BSS patterns were also distinguished. Then we showed how to construct the two frequently used types of BSS in soil fauna and their ecological significances. We introduced research progress on how the BSS of soil organisms respond to environmental gradients and relate to ecological stoichiometry. Limitations and constraints of the BSS application to soil fauna were also noted. In basic theoretical research, we should focus on the correlation of body size with trophic level and energy use in soil animals. Combined with traditional classification method, BSS of soil fauna can be widely used to indicate environmental pollution, ecological restoration, conservation biology, and land use changes.