Abstract: Variations of inlet water flow and riverbed boundary conditions are the dominant factors that precipitate alternating major-minor branches in anabranched rivers, which have different sensitivities to different subtypes. Distinguishing the main factors affecting the alternating major-minor branches of different anabranched reaches is needed to determine/understand the fluvial evolution. Taking the anabranched reaches in the middle of the Yangtze River as reference, 30 generalized schemes are established for the inlet water flow and riverbed perimeter variations. A depth-integrated two-dimensional mathematical model is adopted to explore the effects of the aforementioned factors on major-minor branch alternation. By numerical simulation, a critical branch length ratio of 1.5 is obtained. Hydrodynamic axis shifting is the dominant factor affecting major-minor branches alternation when the branch length ratio is less than 1.5;otherwise, the dominant factor will become the resistance difference between branches, and effects of inlet hydrodynamic conditions on the diversion patterns will weaken significantly.