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We construct a numerical model for a liquid microlens formed by filling a microwell with two immiscible liquids, namely oil and water. The water–oil interface can be actuated as a tunable liquid lens because its curvature is well controlled by applying an external electric field. The contact angle of the oil droplet has the opposite tendency to that of a traditional water-filled microwell because of the repulsion force from the water phase. We study the dynamic interface deformation as functions of time and applied voltage, which typically within 10 ms is good enough as an imaging system for human eyes. In addition, using two different filling liquids provides more possibilities for tuning the focal length.