Abstract: Finite element method was employed to simulate the electric field distributions of a Pt/Ir microelectrode array for opticnerve visual prosthesis. Spatial electric field distributions of microelectrodes with different lengths were analyzed under monopolar and bipolar microcurrent excitements. The effectiveness of the Pt/Ir microelectrode array was validated by an experiment on animals. According to the simulation results, when under a 100 μA current stimulation monopolarly and bipolarly, the maximum points of the electric density all locate at the interface of the Pt/Ir material and the insulation. And as the maximum electric field point being the center, the radius of the effective space under monopolar and bipolar stimulations is approximately 21 and 24 μm, respectively.