Abstract: Flow visualization is made in a 2 D full scale model test section of the ADS target window design, using water as the working fluid. Flow patterns around the simulated target beam window are visualized by laser light sheet with polystyrene spherical pellets (0.5 mm in diameter) as the tracer particles, and recorded with high resolution CCD camera. In the paper the principle and technique of flow visualization with laser light sheet are presented, the obtained flow pattern images are given and discussed.