The Japan Defense Agency is conducting a project to develop a cavitation tunnel called the FNS (Flow Noise Simulator project)(1). The FNS was designed as a large cavitation tunnel with low background noise level to measure the noise of an object. In order to satisfy the low noise level for the FNS, it is important to develop a low noise pump. In the present study, several new design concepts were developed using CFD (Computational Fluid Dynamics) and these concepts and the pump performance were verified by model test. In developing low noise pump, it is important to avoid cavitation generation in all operating conditions. It is also important to reduce blade-passing influence due to blade row interaction between impeller and diffuser. To control unsteadiness by interaction, the axial gap between two blade rows was widened and viscous wake from the impeller was decreased. Many extensive parametric studies (e.g. blade sweep, number of blades) were conducted using three-dimensional CFD computations. The impeller developed for the FNS pump has seven blades, 4.3 m diameter and the stator downstream has nine blades. Several model tests were carried out to verify the design concept of the pump. I was confirmed that the noise level of the new design pump was decreased compared to a conventional industrial pump and efficiency was also improved.