This paper uses space instead of time to lay out typical plots in P. massoniana plantations of different ages in Mengguan Forest Farm in Guizhou Province. Shannon and Levins formulas, Pianka formulas are used to analyze the niche dynamics of dominant species in shrubgrass communities at different development stages. The results showed that: (1) the important values of the same dominant species is different in different forest stands. The important value of Quercus aliena in the 8a and 18a forest stands are 50.89% and 47.32%, respectively, and the important value of Myrsine africana in the 28a forest stands is 50.49% and for 36a, the important value of Smilax china is 50.62%, and the important value of Dicranopteris dichotoma always ranks first in each developmental stage. (2) Q.aliena and S.china have an absolute advantage in the niche width, Vaccinium bracteatum and Castanea seguinii increase in niche width with increasing age, and D.dichotoma niche width increases with the increase in stand age. Microlepia marginata and Deyeuxia arundinacea show a trend of first increasing and then decreasing with the increase of stand age. There is no absolute positive or negative relationship between the importance values of shrub and grass and the width of niche. The same species adapts to the environment and resources in different periods. The utilization capacity is different. (3) Q. aliena and S. china, M. africana and C. seguinii, Stenoloma chusanum and M. marginata, D. arundinacea and Arthraxon hispidus and other species pairs show strong similarities in ecological or biological characteristics. Species with large niche width values are not synchronized with other species niche overlap values.