A novel low-cost,small size variable fiber-optical attenuator (VFOA)device based on variable-focus microlens consisting of two kinds of liquids is put forward,whose basic structure includes a cylindrical precision tube sandwiched between two single-mode fibers (SMFs). Two kinds of immiscible liquids are placed inside the tube(water/oil/water),and constitute a thin liquid (oil) lens medium. The tube is made from electric conductor to acts as an electrode,and the other two electrodes are the right and left connectors connecting the conductive aqueous solution,respectively. The focal distance is tuned by changing the curvature of the meniscus through the effect of electro-wetting,so as to control SMFs coupling light intensity,and ultimately to achieve controlling optical attenuation. Theoretical analysis shows that the range of attenuation values of VFOA is 0~60 dB,and has a very good micro-loss characteristics of wavelength dependence.