River health has great influences on the rise and decline of human society.The assessment of river naturalness can easily tell us whether a river is healthy or not.By taking Tanghe River as an example,the river naturalness was assessed from geographic,ecological and hydrological aspects by using analytical hierarchy process(AHP).The naturalness assessment is made based on the division of the river channel by establishing a river naturalness assessment system composed of 22 qualitative and quantitative indicators.By the final assessment result,the naturalness can be classified as four grades: natural state,near-natural state,degraded state,and artificial state,which coincide with the result from clustering analysis.Analysis of the data indicates that Tanghe River is in the near-natural state on the whole,but some portions of the watershed have been seriously degraded.The naturalness assessment system established in the study may serve as a reference for the assessment of rivers in Beijing suburb and the result from the assessment may provide a basis for future ecological construction of Tanghe River.