The present paper discusses impedance and mobility approach integrated with finite element method (FEM) for free vibration analysis of structural-acoustic coupled systems for irregular geometry. In this method, coupled natural frequencies of any irregular geometry with flexible surfaces with different boundary conditions can be estimated. The proposed hybrid method helps to understand the underlying physics of structural-acoustic coupling in complex geometries. The formulation being in impedance and mobility form, gives more insight in understanding coupled modes of the complex geometries. It is for three dimensional irregular geometries, so it can be used in most of the practical applications where coupled natural frequencies play a vital role. The proposed method is demonstrated for regular and irregular geometry with one wall flexible configuration. The results are corroborated with existing literature data for regular geometry and numerical models for irregular geometry. © 2020 Amogh Nalawade, et al.