The electrode is an important part of cochlear implant system because it affects the current spread and the response of the auditory nerves. In this paper, a new electrode-tissue interface model is coupled with a 3D cochlea and electrode model to simulate the condition of the electrodes in human cochlea is proposed. The effect of incorporating the electrode-tissue interface in a cochlea and the response of the auditory nerves is discussed. Three models are studied, a model of electrode without interface, a model of electrode incorporating the interface effect through an equivalent circuit, and a new model of electrode incorporating a thin layer between the electrode and the scala typmani. The three electrode models were studied using activating functions. Significant different results were found for electrodes with or without taking interface into account. The model results for the electrode model taking into account of the interface effect using an equivalent circuit and a thin interface layer are almost identical.