Abstract: By Nelder spacing trial,the density effect of Acacia auriculaeformis forests is discussed.It is shown that all forests with different densities are not closed when one year old.The smallest densities of closed forests are respectively 3.15,6.20 and 7.00m2 per tree corresponding to 3,5 and 7 years old.After 5 years old,crown growth tends to stabilize.The largest crown growth emerges in the forests with 5.64～6.88m2 per tree occurring in 1～3 years old,while 15.50～18.68m2 per tree occurring in 5～7 years old.Mean stemnumbers of forests are relative to area per tree in power function.When areas per tree of forests are less than 1.0m2,theirmulti stemmed tree percentages are under 10 percent.While it was 100 percent when forest densities weremore than 12.53m2 per tree.