To meet the requirements of fast positioning for disruptive discharge in gas-insulated transmission line（GIL） high-voltage holding test

we put forward a method of condition monitoring and fault positioning by using a low frequency sound field

which provides a theoretical basis for subsequent monitoring of abnormal sound and positioning of disruptive discharge in GIL pipe gallery. According to the characteristics of GIL structure

finite element analysis（FEA） model of GIL was established

and the boundary conditions were set up to simulate GIL of infinite length. Sound modal analysis

steady-state frequency-domain analysis

sound source and background noise analysis

transient time domain analysis of acoustic field were researched. It is demonstrated that fault positioning in GIL using low-frequency sound is feasible and necessary. The results show that the frequency amplitude of sound below 50 Hz is much greater than that of fan noise. Below 40 Hz

the sound pressure level（SPL） at non-acoustic modal nodes decreases with distance increasing.