Pingtan Island is the largest island in Fujian Province and the fifth largest island in China. The invasion of a large number of alien plants has had a profound impact on the local ecological environment. Because the harm caused by alien invasive plants varies greatly between different ecosystems and even in different habitats, the risk assessment index system suitable for one region may not be suitable for other regions. Therefore, it is necessary to establish a risk assessment index system for invasive alien plants on Pingtan Island. Alien plant communities in different habitats were studied by means of quadrat investigation and professional literature review. Some invasive alien species were selected and compiled into a list of invasive alien plants on Pingtan Island, and their species composition, origin, flora, life forms, and habitats were statistically grouped. There were 104 species in 80 genera and 37 families of alien invasive plants. Asteraceae, Fabaceae, Amaranthaceae, and Poaceae were the main families, accounting for 26.7%, 6.7%, 6.7% and 5.8% of the total species, respectively. The geographical components of families and genera have obvious tropical properties, accounting for 51.3% and 66.6% of the total species, respectively. These originated mainly from South America and North America, accounting for 45.5% and 30.1% of the total frequency, respectively. Annual herbs, biennial herbs, and perennial herbs accounted for 84.6% of the total species. Based on a DPSIR conceptual model and an AHP method, an invasion risk assessment of 104 invasive alien plants was conducted. The ecological adaptability, habitat distribution and landscape impact of species were considered in the selection of indicators and the formulation of standards. A total of 23 high-risk invasive species were identified at level I, 37 medium-risk invasive species at level II, and 44 low-risk invasive species at level III. Lantana camara L. had the highest risk score (49), followed by Cenchrus echinatus L. (45), Spartina alterniflora Loisel. (45), and Panicum repens L. (43.5). Suggestions are put forward to prevent the invasion of alien plants on Pingtan Island and to provide a theoretical basis for promoting the healthy and stable development of the ecological environment on the island.