Particle Image Velocimetry (PIV) Fine Flow Field Measurement is a key means for hydrodynamics, noise mechanism and numerical studies. With many years’ experience in the use of PIV measuring technologies and in combination with the objects and environments applied by the circulating channel laboratory, CSSRC has overcome various key difficulties in the underwater 3-D PIV measurement layout, test flexibility and channel suitability, developed a set of underwater 3-D PIV system for circulating channels, successfully applied such a system to “Flow Field Test of Energy-saving Device of 320,000 ton VLCC” and obtained the 3-D flow fields at key locations near the stern energy-saving device, providing powerful test data support for the research and development of energy-saving devices.