A kind of liquid-based and electrically-controlled optical imaging apparatus is provided, which is a cylindrical chamber holding three liquid layers. A kind of insulating liquid is sandwiched between two layers of conducting liquids. A layer of transparent electrode and a layer of insulating layer are coated inside the chamber in turn. Two different external voltages can be applied between the electrode and two layers of conducting liquids, which respectively control two liquid interfaces in the chamber. These two voltages can be matched appropriately to change the focal length and keep the image plane of the apparatus stable simultaneously. Taking the infinite object as an example and based on the Gauss Optics Theory, detailed calculations concerning the relationship between the voltages and the focal length of the apparatus are given. The relevant simulation result that the zoom ratio of the apparatus can be 1∶1.5 shows that such an apparatus is a viable variable focal length optical imaging system.