Western Sichuan's subalpine forests serve as the ecological barrier for the upper Yangtze River. Vegetation restoration in this region mainly involves artificial and natural methods. Analyzing the dynamic changes in species composition and community structure under different restoration modes is crucial for restoring and reconstructing western Sichuan's alpine forests and forming a sound forest management strategy. Using field survey data from the Mountain Ecosystem Positioning Research Station in Maoxian country, this study analyzed the community structure and diversity in Pinus armandii plantation forest, Pinus tabuliformis plantation forest and naturally restored secondary forest from 2005 to 2020. The results showed that: (1) The number of species in the arbor layer increased under different restoration pathways, with increases of 11, 7, and 8 species in the arbor layer of Pinus armandii artificial forest, Pinus tabuliformis artificial forest, and naturally restored secondary forest, respectively. (2) In the Pinus armandii artificial forest, the important value of Pinus armandii decreased from 48.06% to 31.1%, replaced by the native broadleaf species Corylopsis willmottiae, which increased to 21.62% in 2020. The important value of Pinus tabuliformis in the Pinus tabuliformis artificial forest gradually decreased from 43.59% to 29.76%. In the naturally restored secondary forests, the native species Quercus aliena gradually became the dominant species, with an important value of 19.9% in 2020. (3) In Pinus armandii artificial forest, Pinus tabuliformis artificial forest, and naturally restored secondary forest, the temperate zone components accounted for 71.43%, 80.77%, and 84% of the total genera, respectively, exhibiting clear temperate zone characteristics. (4) The arbor level structure in Pinus armandii artificial forest and Pinus tabuliformis artificial forest exhibited a skewed normal distribution, whereas naturally restored secondary forests displayed an inverted J-shaped distribution with a predominance of small-diameter individuals. (5) The heights of arbor layers of different forests showed an increasing trend during the 15-year period, which was as follows: Pinus tabuliformis artificial forest>Pinus armandii artificial forest>naturally restored secondary forest. (6) The Shannon-Wiener and Simpson indices for the arbor layer indicated significantly greater diversity in the naturally restored secondary forest compared to the two artificial forests. The Pinus tabuliformis artificial forest had the highest richness and evenness indices among all four diversity indices in the shrub layer. In the herb layer, the Pinus tabuliformis artificial forest exhibited the highest diversity, with no significant difference in the evenness index. In conclusion, the recovery rate of the artificial forest was greater than that of the naturally restored secondary forest, but the naturally restored secondary forest was more capable of renewal and more conducive to the preservation of diversity. The two artificial forests were gradually replaced by evergreen coniferous forests and the naturally restored secondary forests were replaced by broad-leaved evergreen mixed coniferous forests.