Abstract: Based on the combination of large eddy simulation theory and Lighthill’s acoustic analogy equation, numerical simulation of underwater flow noise is investigated. The calculation model of nozzle and fluid is built up by finite element software, ANSYS. The property of fluid field is calculated by the software of Fluent in the ANSYS. The property changing with time is gotten and dealt with by FFT, then, introduced into ACTRAN. Therefore, sound field of flow noise is calculated. The flow noise of a circular nozzle is carefully investigated. The diameter of the nozzle is 20 mm, and fluid speed is 10 m/s. The frequency range is from 20 to 5000 Hz. The results demonstrate that sound radiation from flow noise is mainly in transition area. The distance between the nozzle and transition area is in the range from 8 to 10 D. Here, D is maximum dimension of the nozzle. Meanwhile, the directivity of radiated noise in transition area is equivalent to a fourth polar point source. Based on the principle of reverberation method, a measurement system of underwater flow noise is built up. The first kind of nozzle is a steel pipe, and inner diameter is 200 mm. The pipe is placed in a reverberation water pool. The dimension of the pool is 9×6×15 (m3). In the pool, there are two parts: one part is flow area; the other part is test area. In test area, there are 32 hydrophones, which are disposed at different depth. The second kind of nozzle is a circular nozzle with coverage formation. The diameters of circular nozzle are 10 mm, 20 mm, 30 mm, respectively. The nozzle is placed in a reverberation water tank, which is made up by steel plates and supported by separated points at the bottom. The dimension of water tank is 3.6×1.7×9.0（m3）. In the top, there are three ducts. The ducts can hinder sound propagation from the tank to the outside, and vice versa. The tank also separated into two parts: one part is flow area; the other part is test area. These actions can protect hydrophones from the knock by the flow. In test area, there are four hydrophones, which are used as a line array to receive the signal induced by the flow. The flow noise source is a tank in high place. And the flow is generated by the gravity. The total sound radiation power level from flow noise is proportional to the 8th power of fluid speed. The results demonstrate that if the nozzle of uniform type, total level of flow noise is only decided by the pressure of flow noise source, and not related to the section area of nozzle. The results are coincided with the simulation.