Alien plants, along with their ecological invasion and negative impacts on indigenous species diversity and ecosystems, are one of the major topics of current ecological research. The background investigation and floristic analysis of alien plants are very important and form an essential database for invasive species research, control and management. In our study these alien plants, mainly collected from the Flora of Shandong Province, combined with a field survey, were studied and analyzed. We also established a floristic database. Our findings are as follows: 1) there are a total of 827 alien species, belonging to 122 families and 416 genera of which 348 species were imported from other countries; 2) a high proportion, 39.0% of the flora in Shandong Province, is accounted for by alien species, of which 21 dominant families largely belong to the Rosaceae, Leguminosae, Asteraceae and Gramineae; 3) the diverse geographical distribution of the genera is characterized by species dominant in the temperate zone which accounts for 52.5% of the alien plants and 44.1% of the plants from the tropics; 4) the origins of alien species and their centralized distribution in Shandong together show the anthropogenic effect and unnatural impacts on the environment and 5) in Shandong Province, alien plants originate more from temperate zones than from any other areas of the world.