The settling basin for oncomelania snails is an important project measure in water conservancy project in combination with schistosomiasis control, which is a sort of construction used to sink and collect oncomelania snails. The measure of setting wall intercepting oncomelania snails in the basin was adopted in recently years to enhance the settling effect. The intercepting wall occupies a part of the passing - water area, then the velocities will increase, and the flow conditions will become more complex. Objective of the paper is to study the intercepting walls function and the effect to the flow structure. A great lot of tests were done under different conditions, including different opening degrees of the intercepting wall and setting one and two intercepting walls. Results show the intercepting wall can obstruct snails in the surface efficiently, but will change the flow. After passing the intercepting wall the water will take snails backwater region, the flow will be accelerated and become more turbulent, and will disturb the settling of the snails. So, it is suggested that only one intercepting wall should be settled near the inlet.