Abstract: In order to study the low-frequency resonant radiation characteristics of the cylindrical liquid cavity with opening at both ends, the distribution parameter model under low-frequency approximation conditions is established. The equivalent vibration model is obtained from the electroacoustic analogy, and the resonant frequency expression without any load is given. Then the “length equivalent method” is used to establish the self-radiation equivalent model and the acoustic field radiation equivalent model of the liquid cavity under radiation conditions. The corrected length, resonant frequency and directivity function of the liquid cavity are given, and the situation under elastic wall conditions is also discussed. Combined with the finite element method, the influence of the characteristic parameters of the circular tube structure on the first-order resonant frequency of the liquid cavity under the condition of rigid (elastic) wall is studied, and the condition that the self-radiation equivalent model met the solution accuracy is given. At last, the piezoelectric effect is used to stimulate the first-order resonance of the liquid cavity, and its acoustic field radiation characteristics are discussed. The comparison results show that the equivalent model calculation value of the first-order resonant frequency of the liquid cavity is in good agreement with the finite element simulation value, and the error is less than 5%. The corrected length of the liquid cavity is 4a/π, and the liquid cavity shows approximately “∞” type directivity under the first-order resonance. This method compares the cylindrical liquid cavity with the opening at both ends to a “liquid rod”, which can be regarded as a part of the structure of a transducer containing a liquid cavity. It can provide a theoretical support for analyzing the working mechanism and radiation characteristics of such transducers from the perspective of distributed parameter model.