Abstract: The Suzhou-Nantong GIL multi-utility tunnel is an innovative engineering project using super long distance GIL with so far the highest voltage level, the largest transmission capacity and the highest technological level in the world. By analyzing the internal structure of the multi-utility tunnel, the physical model of the multi-utility tunnel is built, and two calculating models are put forward based on the acoustic theory and the layout mode of the multi-utility tunnel. The finite element method is applied to calculating the sound field distribution of the multi-utility tunnel, and it can provide a reference for locating the fault position in the tunnel. The results show that for nonuniform sound source, the cut-off frequency of the plane wave in the multi-utility tunnel is around 15 Hz. If the frequency of sound source is below 15 Hz, the sound wave can be rapidly transformed into plane wave during its propagation. Therefore, the fault position can be simply located by TODA (Time Difference of Arrival) method. If the frequency of sound source is higher than 15 Hz, the sound signal should be further analyzed in time domain and frequency domain to determine the appropriate location algorithm.