Double-liquid lens is based on the electro-wetting effect.The focal length of double-liquid lens is mainly decided by the refractive indexes of the two kinds of liquid and the interface between them.The differential equation describing the interface was derived with the aid of Yang function and on this basis,the influences of the physicochemical properties of conducting liquid,insulating liquid and container on the interface were analyzed.Using Matlab and ZEMAX,the numerical solution was calculated by Runge-Kutta method to describe the property of the initial interface.The results were compared with the experimental ones and prove that the double-liquid lens with density difference will shape the interface into an aspheric surface and it can perform better than the one without density difference,which makes double-liquid lens more potential in the field of mini optical system.