Optical switch is an important part of a multi-path electronic switch. We propose an optical switch based on a liquid prism. The device consists of a liquid prism and a non-transparent diaphragm with two holes. In initial state, the liquid-liquid surface shows a shape of the positive lens, the incident light can be focused through the liquid cell and then be blocked by the aperture slot. At this time, the device shows light-off state. When a voltage is applied to one side of the liquid prism, the device shows light-on state. Meanwhile, when voltage is applied to both sides of the sidewall electrodes, the liquid-liquid surface presents the shape of a negative lens and the incident light divergence occurs. At this time, the device expresses the both light- on state. Our experiments show that the proposed device has faster response time (rise time: ~85 ms; fall time: ~140 ms) and higher optical attenuation (~965:1) in adaptive liquid optical switches. The device has potential application in light shutters, variable optical attenuators and optical routers.