Abstract: The spatial characteristics of different types of river networks are analyzed.On the basis of 180° assumption and the acute angle assumption for non-networks rivers,the quantitative decision-making table of automatic determination of flow direction is improved.With the flow directions conflict,the principle of subordination of the minority to the majority is applied.According to the flow directions of channels,accumulated numbers and accumulated lengths of channels on a node,the relations of main streams and branch rivers can be reasoned automatically.On the basis of this analysis,the coding method of tree network rivers are studied.The experimental results show the validation of this algorithm.