Abstract: Conical and pyramidal emitters are two generic field-emitter structures. Due to specific advantages of field emission, both emitters are widely employed to produce electron beams. The main focus of this paper is to analyze the electrical characteristics of both emitters, and further, to highlight the key criteria in optimizing the structures. For this purpose, three-dimensional models were implemented and finite-element analysis was used to investigate the influences of emitter geometries, including shape of emitter, emitter radius of curvature, emitter-anode distance and emitter height, on its electric field distribution and strength. The results indicate that reducing tip radius of curvature and shorting the emitter-anode distance are effective ways to increase the field strength enhancement, while a proper ratio of the emitter height to the emitter-anode distance is also an important factor. In addition, in consideration of both electric field distribution and strength, the conical emitter is suitable for high-resolution, large current-density applications, whereas the pyramidal emitter has better pressure sensitivity.