Abstract: In the subtropical eroded red soil degraded area, the emergence and development of understory vegetation had a complex interspecific impact on the upper pioneer tree population Pinus massoniana. Taking Pinus massoniana of Changting pioneer population as the research object, by collecting the life history data of Pinus massoniana population in different sample plots of understory vegetation coverage in 2018, the static life table of population was established and the spatial pattern of population was also analyzed, in order to explore the mechanism of the difference of population structure and spatial pattern of Pinus massoniana under different understory vegetation coverage. The results showed that with the increase of understory vegetation coverage, the number of small diameter-class Pinus massoniana individuals decreased greatly, and the number of surviving trees increased significantly. Under low and medium understory vegetation coverage, Pinus massoniana population had the highest growth rate, while under high understory vegetation coverage, Pinus massoniana population was difficult to renew, which was a typical declining population. The populations of Pinus massoniana under three coverages were distributed in clusters, but the degree of population aggregation decreased with the increase of understory vegetation coverage. The understory vegetation had a beneficial effect on the growth of medium diameter-class Pinus massoniana by improving habitat conditions, but the shading effect also greatly reduced the number of seedlings. In the long term, the development of understory vegetation made it difficult to renew the population of Pinus massoniana, which would eventually be replaced by other broad leaved tree species and withdraw from the community.