Abstract: Applied the statistical energy assumption and Sommerfeld radiation condition,the radiation coefficient was defined which have the directivity characteristic.Then combined with radiation efficiency,the radiation factor was defined.A real-time calculating method of radiation noise from submerged cylindrical double-shell structures is proposed in this paper.In the method,radiation noise was calculated by radiation factor of shell structures and reconstructing velocity field for outer shell.A test approach was also proposed to measure radiation factor of finite length cylindrical structures.The result of vibration and acoustics tests of submerged cylindrical double-shell show that the calculated radiation noise by this method can satisfy computation requirement of underwater radiation,such as rapidity,directivity and adaptability to operating condition.