Abstract: The competition between zoysia and overseeded perennial ryegrass was studied in Xian, a representative city in north transitional climatic zone, from April to May in 2008 through observing the dynamic change of coverage and density of zoysia and perennial ryegrass. The results indicated that the community pattern of overseeding compound community changed in 2 periods. From April to June, zoysia replaced perennial ryegrass and became the dominant species gradually. After September, the coverage and density of perennial ryegrass increased gradually and became the major species again. Pick and Bige were suitable perennial ryegrass varieties for overseeding and 3.5 g/m2 was the suitable overseeding rate. The competition was mainly affected by the turfgrass genetic characteristics and the external environment and the temperature played a critical role. High frequency and short stubble of mowing changed the light and shadowing conditions and strongly influenced the competitiveness of turfgrass.