Abstract:Plants competes for both above-ground and below-ground resources. However, there are so many conflicting reports regarding the mechanisms of competition in both natural plant population and agricultural plant communities. In this paper, we reviewed some existing literatures dealing with above-and below-ground competitions, including their experimental methodologies as well as the various indices employed in the interpretation of the intensity of both above-and below-ground competitions. It is hoped that this review will serves as a further reference point in which researchers can consider the potential directions for future research in competition studies. Optimal allocation models and theories for both under above-and below-ground competitions, and the variations as well as the trade-off between above- and below-ground competitions, including the effect of heterogeneous resources on these two different spatially competitive environments were compared. Furthermore some of the experimental methodologies in the study of competition such as the divided pot technique, row technique and target technique were reviewed with particular emphasis being placed on their advantages and limitations. In conclusion we suggested that, the following factors viz. the physiological characteristics and developmental status of experimental plants, environmental productivity range and length of competition persistence, should be considered in future studies of competition. Researches on the below-ground competition, process of root interaction and influence are now booming.