Abstract: In order to find out reasonable afforestation density of Acacia mangium×A.auriculaef Ormis, which would bring the best economic benefits, we selected 5 kinds of different densities, used the single factor and the randomized block arrangement experimental design to carry on Acacia mangium×A.auriculaef Ormis density experiment. After 5 years’ observation, the results showed that different densities had a certain effects on diameter at breast height(DBH) and single tree volume of Acacia mangium×A.auriculaef Ormis. With the increase of afforestation density, DBH and single tree volume showed negatively correlation. The DBH was 10.7 cm at the density of 833 trees/hm2, and the DBH was 9.6 cm at the density of 1 666 trees/hm2. When the planting densities were 833 trees/hm2 and 1 000 trees/hm2, the tree volumes were 0.057 566 m3, 0.051 79 m3. The 5 years’ tree volume was 63.922 1 m3/hm2 at the density of 1 666 trees/hm2, separately higher than the other four afforestation density 19.0%, 52.0%, 58.3% and 103.3%. The planting density had no significant effect on tree height.