Three-dimensional imaging system in combination with a digital image processing is developed for determining all-focused and depth mapping properties by using a low-voltage-driving liquid crystal lens with a variable focal length. The continuous focused photo images without the magnification and reduction are taken by applying voltages to the electrodes of the LC lens and tuning a focal plane in a depth direction. The sharp and clear all-focused image can be obtained by processing an image digital filter from continuous focal images. The depth mapping properties can also be derived by our technique.