Abstract: Loudspeaker is commonly mounted on a finite baffle in SPL (sound pressure level) measurement. Formerly, a 3D model must be used for accurate SPL simulate calculation under this acoustic field, which spends huge computation time. An approximate method is proposed, in which the finite baffle is divided into many circulator sectors, then the SPL of the loudspeaker with every circulator sector baffle is calculated by using 2D axisymmetric simulation, and the SPL of the loudspeaker mounted on the finite baffle is finally obtained by combining these 2D simulation results. This method can effectively reduce the difference between simulate calculation and actual measurement. Moreover, the costly 3D model simulation is avoided.