In order to explore the competitive relationship in Platycarya longipes community in Karst area, this study investigated 36 objective trees and 1 502 competitive trees in P. longipes community in Maolan National Nature Reserve. The intraspecies and interspecies competition intensities of P. longipes were calculated combined Hegyis individual tree competition index. The results showed: (1) the intraspecies competition of P. longipes (387.05) was significantly higher than interspecies competition (226.19) (P< 0.01). Its competitive pressure mainly comes from intraspecies competition. (2) There are 59 species of P. longipes associated trees, the species with competition index > 5 were Carpinus pubescens > Pinus kwangtungensis > Liquidambar formosana > Lindera communis > Myrsine seguinii> Pistacia weinmanniifolia > Castanopsis echidnocarpa > Cyclobalanopsis myrsinifolia > Tirpitzia sinensis > Celtis sinensis. (3) The competition index between P. longipes and the whole stand, associated tree species and intraspecies was a power function relationship (CI=aD^b). The larger the DBH of P. longipes, the less the competition pressure was. (4) The competition model predicted that with the increase of the DBH of P. longipes, the competition index of P. longipes decreased within species, between species and the whole stand. When the DBH of P. longipes is greater than theⅠdiameter class (DBH < 3 cm), the interspecies competition pressure becomes smaller, and when the DBH is greater than the Ⅱ diameter class (3 cm≤DBH < 6 cm), the intraspecies competition pressure becomes smaller. When DBH was larger than the Ⅲ diameter class (6 cm≤DBH < 9 cm), the competitive pressure of the whole stand decreased, indicating that P. longipes had higher competitive ability in the middle and small size class. The results showed that P. longipes, as the building species, played an important role in both the development and stability stages of the community, and was more adaptable to the environment in the karst area, and had a great advantage in the evolution of the community, which laid a theoretical foundation for revealing the position and mechanism of P. longipes in the karst forest.