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Abstract: Sound speed is essential for leakage detection in liquid pipelines when using acoustic methods, which can be significantly influenced by gas bubbles generated from leakage. The propagation characteristics and mechanism of acoustic waves in horizontal liquid pipelines containing gas bubbles are studied in detail in the present paper. The effect of sound wave frequency, bubble size and bubble distribution pattern on sound speed is studied through numerical simulations. The results show that the acoustic wave generated by leakage of liquid pipelines containing gas bubbles is a multi-frequency signal, and the energy of the signal is mainly concentrated within 200 Hz. In the low-frequency range, the propagation of sound waves has almost no dispersion in bubbly liquid. Sound speed at a certain void fraction is not constant, which is related to the bubble size and distribution pattern. The bubble size affects the gas-liquid heat transfer equilibrium, during which sound speed is affected. For this reason, a thermodynamic correction factor is proposed, which enables the accuracy of the sound speed calculation to reach 98.2%. What's more, sound speed increases non-linearly with the reduction of the bubble distribution space in the pipeline axial direction. This paper establishes a theoretical calculation model of sound speed based on the bubble distribution pattern in the pipeline axial direction, which is in good agreement with the numerical calculation results. The results of this paper provide the basis for applying acoustic leak detection technology in liquid pipelines containing gas bubbles.