Abstract: In order to provide strategies for prevention and management of alien plants invasion, investigation about the composition and distribution characteristcs of alien plants in Irtysh River Basin were made, and invasion risk levels were assessed. Data about alien plants were collected through field investigation and standard sample survey. This research combined risk analysis methods with the analytic hierarchy process(AHP) to set up an alien plants invasion risk assessment system of Irtysh River Basin. The results show that: (1) A total of 40 alien plants were identified, belonging to 27 genera and 11 families in Irtysh River Basin. Among which Asteraceae and Fabaceae are the main ones. (2) The dominant life type of the alien plants in Irtysh River Basin are herbaceous plants, accounting for 95.00% of the total species, among which annual herbs accounted for 50.00%, and both the vine and woody take 2.50% of the alien plants. (3) The risk level assessment results show that 9 species belong to high-level risk, 12 species belong to medium-level risk, 19 species belong to low-level risk. The conclusions are as follows: alien plants in Irtysh River Basin are not only diverse, but also widely distributed; High-level risk plants must be banned from introduction and scientifically eradicated; Medium-level risk plants should be strictly prevented and monitored in time; Low-level risk plants should be monitored regularly.