In order to predicate the immersion range and degree of the Xingan Navigation and Power Junction on the Xingan section of Ganjiang River, taking the right bank of reservoir as an example, a numerical model of three-dimensional transient flow based on the finite element method was established for the predication and assessment of immersion range and degree of the right bank of Xingan reservoir. Furthermore, based on the simulation model, a comparison was made for the effectiveness of immersion control with two operation conditions including the impervious wall and relief well combined with the impervious wall. When there is no operating conditions, the results indicate that the leakage immersion occurred at the downstream of dam site, the backwater immersion occurred at the upstream, and the immersed transition zone is formed at the dam site. Although the impervious wall can retard the immersion process, serious phenomenon of groundwater immersion will emerge after 275 days. The assessment results showed that the measure combining impervious wall and relief well can effectively control the immersion range, and the impervious wall can greatly reduce the displacement of the relief well. The findings can provide scientific basis for the immersion evaluation and controlling of the Xingan Navigation and Power Junction.