Abstract: A three-dimensional geometrical model of middle ear including tympanic membrane, ossicles, tendoms and muscles was built up here using the serial tissue sections method. The lymph fluid of cochlear could be equivalent to a mass-stiffness-damping model, the physical parameters of the equivalent model were determined according to the published physical properties. Harmonic response analysis was made for the middle ear finite element model. The displacements of the eardrum umbo and the stapes footplate were compared with the experimental data taken from the literature. The reliability of the FE model was confirmed with the comparison. A further study by changing the physical parameters of the equivalent model was made then to observe the effect of the lymph fluid on the sound transmission.