Abstract: This study aimed at the systematically outward branching phenomenon in river channels and the harmonious development between channels and plants under the healthy ecological environments, designed the numerical modelling tests on flow characteristics in a constant curved bend with outward single short-branch based on field river statistics, and investigated the various influences of main-channel curvature ratio and branch outlet on-off condition.The presence of branch had strengthening effects on the downstream main-channel migration potential, and such effects spread towards both the stronger and weaker bending tendencies around the critical bending state (ratio of curvature radius to channel width equals to 3.0).The presence of branch caused the wane and wax of "the strong and positive vortex zone" near the bed around the outer-bank side and "the weak and negative vortex zone" near the surface around the inner-bank side in the downstream channel, and the final neutralization of the these two.The outflow state of branch led to the significant decreases of helical flow strength at both the cross-sections along the downstream channel and horizontal sections near the overall channel bed, and the significant increases of helical flow strength at the cross-sections along the upstream channel under the strong bending conditions.The shear stresses tended to decrease at the bifurcation head and become larger around the local confluence zone, particularly, when freeing the branch flow, both of them would significantly increase, and the shear stresses at both the downstream inner sidewall and the most downstream quarter of bend bed would drop to the extremely low value states.This study provided the fundamental hydro-informatic supports to harmoniously physical space design for plants development in river system.