In 2021, following the establishment of the Hainan Tropical Rainforest National Park, specific sectors of the artificially managed woodlands within the park ceased operational activities, entering a state of secondary natural succession. This shift has given rise to a more profuse understory vegetation compared to prior years, necessitating further exploration. To gain insights into the secondary natural succession status of the artificial forests and their adaptive strategies to the environment, a study was executed in the rubber tree plantation within the Hainan Tropical Rainforest Park. A total of 390 plots, each measuring 10 m × 10 m, were instituted. Expanding upon a comprehensive survey of vegetation distribution within the Hainan Island park, the research focused on scrutinizing the composition of understory vegetation and the correlation between plant community characteristics and environmental factors in the designated area. The findings disclosed that: Vascular plants were systematically categorized into 123 families, 455 genera, and 808 species. This comprises 21 families, 31 genera, and 62 species of ferns, 3 families, 3 genera, and 4 species of gymnosperms, and 99 families, 421 genera, and 742 species of angiosperms (encompassing 15 families, 69 genera, and 120 species of monocots, and 84 families, 352 genera, and 622 species of dicots). Redundancy analysis (RDA) of plant species diversity indices and environmental factors in the study area illuminated 18.5% of the variability in species diversity beneath the rubber tree canopy. Monte Carlo random permutation tests identified eight environmental factors significantly influencing understory species diversity in the rubber tree plantation (P<0.05), with the most salient effects observed for the average temperature in the driest quarter, average temperature in the wettest quarter, mean diurnal temperature range, and the influences of mixed vegetation, diameter at breast height (DBH), elevation, annual precipitation, and precipitation in the driest quarter (P<0.01). The study posits that understory plant diversity is subject to the interactive effects of multiple environmental factors. Specifically, temperature and precipitation emerge as pivotal factors influencing understory plant diversity, with adverse impacts observed under conditions of heightened temperature, increased humidity, and drought. Additionally, altitude-related thermic conditions and the condition of artificial forests, including DBH and mixed vegetation, assume noteworthy roles in shaping understory plant diversity.