Abstract: Imperata koenigii was artificially planted into young tall fescue (Festuca arundinacea) turf. The tillering, depth and meristematic capacity of roots, and biomass were determined. Root and shoot competitiveness of the two species and traits of young tall fescue were studied. The intrusion volume of I. koenigii had a significant effect on the relative yield of root and shoot, total relative yield, and attack index of F. arundinacea. There was an antagonism between the two species. Direct competition for the same resources existed between the roots. I. koenigii had obvious competitive advantages because of its positive attack power of roots and shoots. The invasion of I. koenigii significantly affected the tillers and height of F. arundinacea. There was a significant negative correlation between turf quality of F. arundinacea and intrusion volume of I. koenigii, and a significant positive correlation between turf quality of F. arundinacea and other indexes except plant height. Weed control, inhibition of plant height, meristem promotion and competitiveness increment were basic requirements and necessary means to improve the quality of tall fescue turf.