Over the past few decades, microfluidic droplet transport based on the electrowetting effect has received considerable attention owing to its wide diversity in various kinds of scientific areas. However, many aspects of its physics are still not completely understood, which partially limits its application efficiency and has become the restriction on its further development. In this work, droplet transport in a parallel-plate electrowetting-based digital microfluidic device has been carefully studied via a numerical model. A finite volume formulation with a two-step projection method is used for solving the microfluidic flow on a fixed computational domain. A coupled level-set and volume-of-fluid (CLSVOF) method is used for capturing the free surface of droplet. Contact angle hysteresis is implemented as an essential component of electrowetting modeling and the viscous stress exerted by the parallel plates is evaluated by a simplified viscous force scheme. The transport process has been simulated with two different electrode designs, namely 'Square Electrode' and 'Stripped Electrode'. Excellent agreement has been achieved between the numerical results and the corresponding experimental data. The droplet length and transport speed of the two designs have been numerically compared and analyzed. It has been found that both the transport speed and stability can be greatly enhanced by the 'Stripped Electrode' design, which can be adopted for enhancing droplet transport efficiency in a large number of microfluidic applications using electrowetting effect as the driving mechanism.