The electric field distribution of modified interdigitated electrodes structure at high fields is analyzed through simulation, and the feasibility that the structure can be used in electro-optic polymer thin film devices is verified. Due to the non-uniform electric field during poling in the thin film devices with interdigitated electrodes, the three-dimensional electric field distribution model related with the electrode gap and the polymer thickness is established, and the average electric field is obtained at different poling voltages. For the changes in the structure of the thin film device with the interdigitated electrodes, the transmission-geometry ellipsometric technique based on device with sandwich structure is modified. In addition, the experimental results of electro-optic coefficients of the devices of the interdigitated coplanar electrodes and the sandwich structure are compared under the same electric field. Experimental results show that changes in the structure of thin film device will not cause the resulting electro-optic coefficients changed.