Based on the signal model of ear canals, a novel method for solving the inverse problem of estimating the unique solution of the ear canal area function and the eardrum reflection coefficient given the acoustic input impedance at the entrance of an ear canal is presented. Up-sampling techniques to improve the accuracy of the estimates are also presented. The performance of this method and factors affecting the accuracy of the estimates are investigated via simulations. It is found that the accuracy of the estimates is limited by the measurement bandwidth of the given ear canal input impedance. In the audio frequency range, the estimates obtained approximate well to the true ones. To obtain more accurate estimates, a wider measurement bandwidth of the ear canal input impedance is required.