There are complex interrelationships and internal mechanisms among bed form, sediment transport and flow structure in natural river , in particular in confluent river. The experiments were conducted in flume including different cases, e.g., without branch flow, branch flow with clear - water， branch flow with both water and sediment. The stable bed morphology in every case was measured and analyzed with different discharge ratios q* of the branch channel flow Qb to combined tail - water flow Qt. The characteristics of variation of bed morphology of main channel under above - mentioned cases were revealed. 