Xanthium italicum Moretti has been invading farmland of Glycyrrhiza uralensis Fisch, but little is known about its impacts. Therefore, interspecific competition between the two species has been studied to provide an experimental evidence for evaluating the invasibility and effect of the presence of X. italicum on the G. uralensis population in farmland. Pot experiment was carried out and common soil water and fertilizer condition of the cultivated G. uralensis were simulated. Two treatments, monoculture and mixture of the two species, were conducted and a replacement experiment was adopted. All the plants were harvested at the end of the growing period of X. italicum, then growing status and biomass of each plant and glycyrrhizic acid concentration of G. uralensis between the two treatments were compared. The relative competitiveness ability of the two species was compared by relative yield, relative competitive intensity and aggressivity. The results showed that, compared with the monoculture treatment, the vegetative growth and seed production of X. italicum were significantly higher in the mixture treatment. The height, crown width and seed number of X. italicum under the mixture treatment increased by 13%, 27% and 56% respectively compared to those under the monoculture treatment. However, the individual growth and development of root nodule of G. uralensis were significantly inhibited as they grew together with the alien plant, because compared with the monoculture treatment, the height, crown width, total root length, total root surface area, average root diameter and the number of root nodules of G. uralensis under the mixture treatment decreased by 35%, 45%, 55%, 63%, 19% and 76%, respectively. There were three pieces of rhizomes per individual of G. uralensis on average under the monoculture treatment, but its rhizomes development was completely inhibited while being planted together with the invader. The biomass of X. italicum in the mixture treatment was significantly higher, and its root, stem, leaf, fruit and total biomass increased by 84%, 73%, 84%, 73% and 77%, respectively compared with those under the monoculture treatment. However, the mixture treatment significantly reduced the biomass and glycyrrhizic acid accumulation of G. uralensis, since its root, stem, leaf, total biomass and glycyrrhizic acid concentration decreased by 72%, 80%, 65%, 71% and 63%, respectively. The relative yield of X. italicum in the mixture treatment was more than 1, while that of G. uralensis was less than 1, which indicates that the pressure of intraspecific competition of X. italicum was greater than that of interspecific competition from the G. uralensis, and the pressure of intraspecific competition of G. uralensis was less than the pressure of interspecific competition from the X. italicum. Under the mixture treatment, the relative competitive intensity of X. italicum was less than 0, and its aggressivity was greater than 0, while the relative competitive intensity of G. uralensis was between 0 and 1, and its aggressivity was less than 0, which indicates that G. uralensis is less competitive than X. italicum when the two species coexist. In summary, the exotic plant X. italicum is of more strong competitiveness than G. uralensis, and the invader has a strong impact on the yield and quality of the licorice.