Abstract: The identification of the underwater radiated sound field of a plate and cylindrical shell were studied numerically by using the phase conjugation method.The normal velocity distribution of the structure was reconstr ucted by two different methods after obtaining the surface pressure distribution.One method was based on the pressure gradient and only required the dimension and the location of the structure in the sound field,the other was based on the surface impendence relationship of the structure vibration and the surface pressure distribution.The results show that the pressure gradient method can get the approximate distribution of the surface normal velocity and is simple to implement even if the surface impendence relationship is unknown.The method based on the surface impendence relationship achieves more accurate identification results of the surface normal velocity.