Electrowetting-on-dielectric (EWOD) is foreseen as an innovative way to realize artificial-intelligence (AI) laboratory. However, EWOD is still a research tool and not for widespread application because of the high actuation voltage. Electrode shape optimization is an effective method to reduce the actuation voltage. In order to determine the impact of electrode shape on driving threshold voltage, the mechanical model of droplet actuation is established based on the minimum energy principle. The larger the contract area and effective three-phase contact line between the droplet and electrode are, the larger the driving force applied on the droplet. Based on this, we optimized the structure of the crescent electrode with lower driving threshold voltage. When the ratio of the equivalent diameter of the semilunar surface to the side length is 1:1, both the value of contact area and effective three-phase contact line are maximum, the velocity of droplet is fastest, and the threshold voltage is minimum which is 21V.