Abstract: Niche breadth, niche similarity proportion and niche overlap of 23 undergrowth populations of Platycladus orientalis and Robinia pseudoacacia community were analyzed. Results show that niche breadthes of Oplismenus undulati-folius, Vitex negundo, Grewia biloba and Carex duriuscula are relatively wider than those of the other species, while regenerated seedlings of Platycladus orientalis and Robinia pseudoacacia own narrower niche breadth. Niche similarity proportion and niche overlap of the 23 undergrowth populations are relatively smaller, indicating that competition for environmental resources is not fierce among the different populations. Thus niche differentiation can be enhanced by improving planting arrangement.