Abstract: Aerial seeding is a very important way of afforestation, and China aerial seeding area takes up the first place in the world.Compared to tree planting, aerial seeding has some shortcomings: the heavy density, enclosure management after the implementation of afforestation, early canopy, and poor development of understory vegetation. In this paper, using the method of space generation time, we selected three ages of aerial seeding forests: 10, 17 and 25 years old as the research objectives, and analyzed their compositions of understory vegetations, the dominate species, vertical stratifications and the changeable of species diversities. The results show that there exists a minor differences in the number of species among three different ages of aerial seeding forests, the number of species of understory vegetation in 10,17,25 years old forests were 27,24 and 20 respectively. The dominate species in 10, 17 and 25 aged forests are all Spiraea pubescens+Spiraea trilobataCarex lanceolata. Shrub layers height increases as the age of the forest increases. The 17 years old aerial seeding forest has the maximum herb layer height. Shrub and herb layers coverage first decreased and then increased when the trends age increases; the index of ShannonWiener of 10, 17 and 25 years old aerial seeding forest of understory vegetation is 2508,0824 and 0776, and Pielow index is 0779,0256 and 0241 respectively. The diversity of understory vegetation declines when the forest gets older, shows that, the arber layer gives a rising pressure to inhibit the growth of the understory vegetation, so it is necessary to manage aerial seeding forest at the appropriate time to control the forest structure is needed.