Abstract: The free-flooded-ring transducer with slow waveguide is the underwater acoustic transducer which is composed of the free-flooded-ring vibrator and slow waveguide. Such transducer utilizes the modulating effect of the slow waveguide on the sound field and the directivity of transducer is effectively improved. However, the sound field of such transducer can not be solved analytically by the Helmholtz integral formulation. In this paper, numerical solution is found through the use of the Helmholtz integral equations in the form of the finite surface element. The numerical and experimental results are essentially in agreement.