An estuarine branching system has four skinds of vertices, i.e., forks, junctions, knots and outlets, and thirteen kinds of links correspondingly. Some concepts of theory of topology and graphs have been introduced in this paper to make further expression quantitatively to the topo-logic properties of estuarine branching system. After redefining the: recombination factor, or the ratio of number of junctions and knots to number of forks, this paper points out the recomb- ination factor varies from zero to one nearly, with the extent of bifurcating and rejoining of an estuary. Ninteen natural branching estuaries have been studied in details. The results show us the recombination factor ranging from 0.25 to 0.93, which is related to various kinds of vertices and links, deltaic area, the exterior angle of an estuarine branching system to a certain extent. The most frequently appeared vertices in a natural estuarine branching system are forks and outlets, while links are ff, fj and fo. Tlhe most scarcely appeaxed vertices are knots, while links are kk and ko. Finally, in accordance with the principle to combine the cause, plain feature and channel changing characteristics together of a branching estuary. this paper proposed that four branch-ing models: less-branching, much-branching. complex networks and wandering. The properties of topology of each model have beem studied quantitatively.