Based on three afforestation experimental plots in Yanxi State-owned Forest Farm, Changtai District, Zhangzhou City, Fujian Province, namely the pure forest of Mytilaria laosensis, the mixed forest of Mytilaria laosensis and Eucalyptus urophylla × grandis, and the pure forest of Eucalyptus urophylla × grandis, the growth conditions of the stands such as the diameter at breast height, tree height and canopy density of the trees under the three afforestation models were measured from 2017 to 2021. The main species and coverage rates of shrubs and herbaceous plants under the forest were determined in 2017, 2020 and 2021. The results showed that the fast-growing performance of Mytilaria laosensis was good. The various indicators of Mytilaria laosensis in the mixed forest had slightly increased compared with those in the pure forest. The diameter at breast height, tree height and volume of Eucalyptus urophylla × grandis in the mixed forest had increased by 9.68%, 6.29% and 24.91% respectively compared with those in the pure forest of Eucalyptus urophylla × grandis, and the growth effect was obvious. The average annual growth rate of each index of the two tree species in the mixed forest was basically higher than that of the corresponding pure forest. With the extension of afforestation time, the coverage rate of miscellaneous shrubs and herbaceous plants under the pure forest and mixed forest of Mytilaria laosensis had significantly decreased, with the decline rates all exceeding 85 percentage points. Therefore, the ability of Mytilaria laosensis to regulate undergrowth vegetation was superior to that of Eucalyptus urophylla × grandis. It could be used as a preferred tree species for forest construction in the study area. Through a scientific mixed planting model with Eucalyptus urophylla × grandis, the ecological functions among tree species can be complementary, thereby promoting the improvement of regional forest quality and the optimization of ecological benefits.