Numerical simulation of a zero-leakage microvalve is investigated where a liquid droplet is used as a gate to regulate the flow in a T junction. The droplet gate is activated by changing its surface tension via an applied electric field. Numerical simulation of the droplet actuation is considered where the effect of electrowetting is imposed in the form of a modified boundary condition at the contact line. Numerical simulation is used to predict the droplet behavior and to design the valve. It is found that the pressure breakdown of the microvalve is significantly affected by the geometry of the T junction corners. It is expected that such a microvalve design will improve the sensitivity and performance of a wide variety of microfluidic devices.