Abstract: Recently the finite element method has been applied to the engineering acoustics. For example, it has analysised the acoustics field in irregular shaped room, the forced vibration problem of the electroacousitic transducer, and applied to evaluated performance of the reactive muffers. In this paper the finite element method is demonstrated to applied for the solution of the wave equation. We determined the frequencies of normal modes of the irregular shaped room. By comparing the results for the linear function and cubic polynomial function and the convergences of eigenvalue. Calculating on two dimensional models. It has proved that the irregularity of the room shape is not influence the diffuse sound field in the room.