Optical beam steering is an essential element for optical communications, laser detection, ranging (LADAR), and solar cell. Electrowetting, which is a phenomenon that changes the contact angle of a liquid on a solid surface using electrical force, can be used to control optical beam. This device is called electrowetting-driven micro prism (EMP). Prism size, viscosity of the ambient fluid, electrical signal, and interfacial tension can affect the performance and stability of EMP. In this study, the effects of these factors on meniscus dynamics in EMP are investigated both experimentally and numerically. Especially, we explore how viscosity and electrical signal affect the switching time (i.e., the time to reach the either peak or equilibrium) and the maximum contact line velocity. Finally, we observe the entrapment of ambient oil and small oil drops formed by film instability in EMP system and investigate the effects of viscosity of the ambient fluid and electrical voltage on the size distribution of oil drops.