Plant population dynamics of a human-impacted masson pine (Pinus massoniana) plantation was studied in Dinghushan Biosphere Reserve in Guangdong for 5 years from 1990. Twenty paired plots with total area of 4 000 m² were investigated in plots of harvesting under-story, ground cover, and litter as the local peasants did for fuel annually once or twice, and in undisturbed plots as control. The results indicated that understory coverage and the shrub coverage in undisturbed plots increased annually, but those in disturbed plots remained little changed．However,the coverage of herbs was slightly increased before 1 992，and then decreased markedly in undisturbed plots，while that in disturbed plots was on the contrary． The coverage of main shrub and herb species was also measured． Species number of un derstory plants decreased annually from 41 to 30 in un disturbed plots． but that in disturbed plots remained more or less stable， only 2 species lost．The result showed that appropriate disturbance in understory of masson pine plantation could maintain species abundance，an d exhibited positive efect on natural regeneration of pine tree，but negative impact on pine growth． The possible succession of open masson pine forest toward pine-broadleaved mixed forest is discussed.