This paper deals with the physical analysis and the experimental verification of splitting a droplet in an open microchannel (i.e., in a gap between two plates) by electrowetting forces. We discovered there exist criteria beyond which the droplet simply cannot be split by controlling the electrowetting. Based on the criteria, we fabricated the testing devices where an electrowetting principle was used to split a liquid droplet and made the experimental verification for the criteria. The channel gap size, the droplet size, and the contact angle change by electrowetting are important parameters in splitting a droplet. The small channel gap enhances the necking of the droplet, helping the splitting process. Higher applied voltage induces larger change in contact angle and consequently enhances the splitting process as well. Most importantly, the droplet cannot be split if the channel gap is too large for the given droplet size and EWOD mechanism.