Abstract: A composite replacement experiment was carried out to analyze the effect of five substitution ratios of Imperata koenigii on competitiveness and growth potential of three species of cold season lawn grass (tall fescue, Kentucky bluegrass, perennial ryegrass). Single plant biomass, relative yield, total relative yield, attack and competitiveness, plant height, tiller number, pseudostem and root traits, among others, were determined. I. koenigii substitution had an antagonistic effect on the lawn grasses. The substitution ratio of I. koenigii had a highly significant effect on relative yield and total relative yield of the 3 species (P<0.01). With increasing substitution ratio of I. koenigii, the attack and competitiveness indexes of the lawn grasses were gradually reduced. Grass species was the main factor determining attack and competitiveness of lawn grass, and the three species tested ranked in order: tall fescue>Kentucky bluegrass>perennial ryegrass; the next most important factor was the substitution ratio of I. koenigii. The substitution ratio of I. koenigii had a significant effect on tiller number, pseudostem traits and root characteristics of the three lawn grass species (P<0.05). The ranking of the species for regeneration ability was Kentucky bluegrass>perennial ryegrass>tall fescue, while the ranking for root length and biomass was perennial ryegrass>Kentucky bluegrass>tall fescue. Attack and competitiveness index of ryegrass in the seedling stage was significantly greater than for tall fescue and Kentucky bluegrass (P<0.05). The stress impact of I. koenigii substitution on roots of perennial ryegrass was significantly greater than that of the other two species (P<0.05), resulting in a decrease of perennial ryegrass growth potential. The competitiveness and attack of tall fescue was lower, than the other lawn grasses and I. koenigii substitution enhanced the stem and root traits of tall fescue to significantly lower than those of perennial ryegrass and Kentucky bluegrass. Therefore, tall fescue had a very high growth potential. These results indicate that I. koenigii presence in the three species of lawn grass studied, necessarily led to damage to sward population composition and structure of the lawn grasses. Management measures should applied to prevent I. koenigii invasion of lawns in order to improve lawn quality and persistence.