In order to investigate the effects of interspecific competition on the growth of Typha domingensis and Phragmites australis, a pot experiment technique was designed to study the interspecific competition characteristics of T. domingensis and P. australis under different root barriers, including plastic barrier (complete root separation, no interaction and no substance exchange), nylon mesh barrier (partial root separation, no interaction and substance exchange) and no barrier (no root separation, root interaction and substance exchange). The root morphological characteristics and above-ground growth were analyzed to explore the differences of interspecific competition between T. domingensis and P. australis. Results showed that (1) P. australis had obvious disadvantage in nylon mesh barrier and no barrier treatment. Compared with plastic barrier, the total biomass, plant density were 39.14%, 49.41% and 82.08%, 79.22%, total root length, root surface area and root volume of P. australis were 40.53%, 44.84%, 62.52% and 85.7%, 82.45%, 89.67% significantly lower under nylon mesh barrier and no barrier treatment, respectively. And plant height, stem diameter and leaf number in our study were affected by root barrier treatments, following the order of no barrier > plastic barrier > nylon mesh barrier. (2) The total biomass of T. domingensis in the nylon mesh barrier and no barrier treatment was higher than those in plastic barrier treatment, but the difference was not significant. However, Plant density and plant height of T. domingensis in the nylon mesh barrier and no barrier treatment were higher than those in plastic barrier treatment, and the difference was significant (P<0.05). Compared to plastic barrier, the total root length, root surface area and root volume of T. domingensis were increased by 57.93%, 26.5% and 8.04% in nylon mesh barrier, respectively, but decreased by 11.57%, 14.92% and 11.39% in no barrier treatment, respectively (P<0.05). Although the interaction of root promoted the growth of the root of T. domingensis, and the roots interaction are stronger, more disadvantageous to the growth of them. (3) In different root barriers treatment, obvious changes were also found between T. domingensis and P. australis. In no barrier treatment, the biomass and the plant density of T. domingensis were 1.7 times and 6.74 times higher than that in P. australis, and increased 6 times compared with plastic barrier. The study indicated that the roots interaction between T. domingensis and P. australis significantly weakened the reproductive growth of P. australis, and increased the root tillers of T. domingensis. (4) The interspecific interaction index (RII) analysis also showed that P. australis exhibited inhibitory effect (RII was negative) and T. domingensis exhibited promoting effect (RII was positive) under nylon mesh barrier and no barrier. The root interactions can inhibit P. australis, which has a strong impact on plant adaptation and plant community reproduction. It also shows that root not only play a key role in uptake of water and nutrients from soil, but also play an important role in interspecific relationships. The results provide a technical support for the biodiversity conservation and protect the ecosystem function by controlling the growth of P. australis through interspecific competition.