The theory on voltage-tunable multiple liquid crystal filters is discussed, and designing examples are given. The multiple filters composed of three single liquid crystal filters are mainly discussed. The three filters in the system may have the same thickness or proportional thickness. Both forms are effective. The filters having proportional thicknesses can change the transmitted wavelength by tuning the voltage, and the scope of the transmitted peak is 400～800 nm, covering the whole visible spectrum. The filters with the same thickness can be used to select certain desired wavelengths from multiline spectrum.