Abstract: Accurately calculating the large and complex noise field distribution of indoor substations and then evaluating the noise re-duction effect of noise reduction measures are the key problems to solve the noise pollution of indoor substations. To this end, combining the advantages of acoustic finite element method (FEM) for solving complex sound fields with good conver-gence and high precision, and the advantages of acoustic boundary element method (BEM) for dimensionality reduction in solving large sound fields, we proposed a noise field solution algorithm for indoor substations based on acoustic FEM-BEM. First, the sound-structure coupling model of the sound source inside the substation was established, and the acoustic-structure coupling response under the action of reverberation noise was solved by using acoustic FEM. Then, based on the acoustic FEM-BEM coupling theory, the displacement and stress loads generated by the acoustic-structure coupling excitation of the structural elements at the inner and outer coupling boundaries were solved. Finally, according to the external acoustic wave diffusion model excited by the sound pressure and stress load, and based on the conventional Gauss numerical integration method, a two-dimensional acoustic integral equation of BEM in the external space acoustic domain was established to solve the external sound field. The algorithm has been successfully applied in the solution and analysis of the noise field of a 110 kV indoor substation in Hunan, and the error with the measured value is 3.61%~4.87%.