Abstract: Coplanar-grid detectors, which have been developed recently, can effectively overcomethe problem of poor hole collection in detectors. Thus the energy resolution of gamma ray can be greatly improved. Finite elements analysis is utilized for simulating the potential distribution of the coplanar-grid detector under different electrode models by varying the widths of grid, gap and theposition of electrodes. In addition, the influence of edge effects resulting from the unsymmetricalelectrodes on induced charge is discussed. In this way, the geometry of electrodes for coplanar-grid detectors is optimized and thus the energy resolution of detectors could be further improved.