Vegetation is a factor influencing soil erosion significantly, as in turn soil erosion has great impacts on vegetation restoration. Pinus massoniana forests in eroded red soil region of southern China are subject to scarce undergrowth and severe soil erosion. It is therefore of great importance to study the relationship between undergrowth features and soil erosion in order to reveal the soil erosion process and the vegetation restoration mechanism of P. massoniana undergrowth. This study selected five hilly P. massoniana forests in Datian Town of Ganxian County in the eroded red soil region developed from granite in southern China. Each hill was surveyed along one belt transect from the upper to lower slope. There were totally five belt transects and fifteen sample plots of 10 m ×10 m. The investigation and measurement of landform, soil, vegetation and erosion gully were carried out in each sample plot. The relationship between vegetation features and soil erosion was analyzed statistically based on the observed data. The results showed: 1) The canopy density of P. massoniana forest in the eroded red soil region developed from granite was at a low level; the growth of woods was in poor condition and the total vegetation coverage was only 36.9%. 2) The undergrowth biomass of shrubs and herbs were low, and the richness, diversity and homogeneity were limited as well. 3) The undergrowth vegetation is mainly herbs dominated by Dicranopteris dichotoma whose biomass amounted for over 75% of the total herbs. 4) Rill and shallow gully erosions were serious which had a soil loss of 71.2 mm thick per unit area. 5) The development of eroded gullies and slope position were significantly correlated. There was a marked difference in micro-environment between eroded gullies and slopes, especially in terms of soil density and moisture. 6) The soil erosion amount under P. massoniana forests has an inhibitory effect on the vegetation restoration, while the growth of gully density increases the richness, diversity and uniformity of shrub and herb species.