Microholes are widely used in industrial products, such as engine nozzles and filters for biomedical industry. Electrical discharge machining (EDM) is one of processes to drill microholes in alloy with high aspect ratio. However, the achievable aspect ratio of a microhole by micro-EDM is limited. To improve the aspect ratio of a microhole drilled by micro-EDM, the planetary movement of electrode is applied during machining. It was found that the machining efficiency of microhole drilling can be further improved by proper setting of planetary movement of electrode, such as the electrode feed rate and movement speed of electrode in XY plane. In this paper, a theoretical model is proposed to optimize parameters of the planetary movement of electrode. Microholes are drilled aided with planetary movement using different machining parameters to verify the model. Experimental results agree with theoretical values, which indicate the validity of the proposed model. This model provides certain theoretical basis for machining parameter selection when microholes are drilled aided with planetary movement.