With the application of the WRSIS (wetland-reservior-subirrigation system) concept in the Midwest USA and recently in China, an improved design and evaluation approach is needed. An experimental WRSIS site established in Guilin, China, consists of a wetland constructed within an existing paddy scheme. In this paper, we present a simulation analysis approach on the hydraulics of the Guilin constructed basin design, and alternatives to the original design focused on basin shape, flow barriers within the basin, vegetation density and distribution, etc. A SST k-ω model is applied to simulate the flow hydraulics within the constructed basin. Variables influencing hydraulic characteristics have been used to predict flow characteristics within the basin, with particular interest in inlet and outlet conditions, flow barrier presence and placement, and vegetation density and distribution. Flow analysis results are further analyzed using a multi-parameter probabilistic model, which helps us infer individual correlations existing between the variables. Modeling results have led to proposed changes in constructed wetland basin designs, based on alternative placement of flow barriers, vegetative resistance, and other design parameters influencing the overall mass flow rate. This approach has been developed to serve as research, engineering design and evaluation methodologies.