Abstract: As one of the key soil invertebrates, earthworms can greatly impact soil processes, and thus was named as “ecosystem engineer”. Earthworm activities such as feeding, digestion, excretion, and burrowing, facilitate the formation of various drilosphere in their guts or soils around, through which they alter the biological, chemical and physical processes of the ecosystem. Earthworms act as consumer, decomposer and modulator in ecosystem. The ecological functions of earthworm include: (1) effects on key soil ecosystem processes such as decomposition of soil organic matters and nutrient cycling; (2) effects on soil chemical and physical properties; and (3) interaction with plants, microorganisms and other animals. Earthworm activities and their functions in ecosystem are determined by various factors such as ecological groups of earthworms, population size, vegetation, parent materials of soil, climate, time scale, and history of soil utilization. The development of earthworm ecology was constrained by the complex feature of soil, the scarce knowledge of natural history and biogeography of earthworms, and the low efficiency of approaches in field manipulation of earthworm community. We suggest that new technologies such as the C and N isotope technique for nu-trient cycling and the image analysis approaches for soil micro-structure should be applied on earthworm ecological research in order to better understand the functions of earthworms.