Abstract: The balanced armature receiver (BAR) has the characteristics of small size, high electro-acoustic transform efficiency and high sensitivity. Based on the lumped parameter model, this paper point out that the movement of balanced armature will affect the back EMF and magnetic force and proposes a numerical simulation method for BAR to obtain its sound pressure level and impedance based on COMSOL Multiphysics. Firstly, the steady state analysis of the magnetic field characteristics of BAR is carried out, and the driving force and back-EMF, which can vary with the movement of the balance armature, are calculated. Then, the coupling models of magnetic, mechanical and acoustic fields are analyzed in frequency domain, and finally, the sound pressure level and impedance are calculated. comparison between simulated and measured results shows that they are basically consistent.