Taking the masson pine plantation 10a, 20a, 30a and 36a of mengguan forest farm in central Guizhou as the research object, by adopting the method of replacing time change with space change, we analyzed the dynamic characteristics of diameter scale structure and species diversity in the development process of masson pine plantation by setting 12 typical 20 m by 20 m plots. The results showed that: (1) the diameter grade structure of masson pine plantation was different at different age stages, with singlepeak structure at 10a stand and multipeak structure at 20a, 30a and 36a stands. (2) There are a total of 53 species in 53 genera and 35 families of plants under the forest, including 24 species in 24 genera and 16 families of shrubs, 29 species in 29 genera and 20 families of herbs, with relatively rich species. Species composition of stands of different ages: 20a stands > 10a stands > 30a stands > 36a stands. (3) Species richness index of masson pine firstly increased and then decreased with the increase of forest age. Shannnwiener index, Simpson index, Pielou evenness index and Alatalo evenness index showed the opposite trend between 10a and 30a, and the same trend between 30a and 36a.