Coarse woody debris (CWD) is an important structural and functional element in forest ecosystem. In this paper, the definition, dynamics, and role of CWD in a forest ecosystem were overviewed. CWD include all woody debris above and under the ground with a diameters > or = 2.5 cm, and mainly comes from the dead trees resulted from competition and disturbances. The biomass of CWD changes like "U" form along with the development of a forest community. The decay rate of CWD is determined by the compound course of the respiration and natural fragmentation. Insects and microorganisms play an important role in the course. CWD basically has two functions in an ecosystem. One is as the nutrition pool for some living creatures, and the other is that the large CWD can form some special habitats for animals and plants. Conclusively these two functions are helpful to reserve the biodiversity and the integrity of ecological process in a natural ecosystem. Gaps are formed while dead trees falling down, and all gaps in a forest succeed one another randomly in the development of a forest ecosystem, which pushes the inner circulation of the forest. Because of the vital roles of CWD in a forest ecosystem, much more attention should be paid in the management of forest ecosystem.