1. An auto-focus system using multiple lenses, adapted for an image capture device having a first lens, a second lens, a first lens driving module and a second lens driving module, and the auto-focus system comprising: a repeated pattern detection module, configured for receiving a first image and a second image from the first lens and the second lens, respectively, and detecting whether a repeated pattern appears in a preset focus area of the first image and the second image; a first focus module, configured for calculating a focus depth according to the first image and the second image when the repeated pattern detection module judges that the repeated pattern does not appear, and controlling the first lens driving module and the second lens driving module to drive movement of the first lens and the second lens for focusing; and a second focus module, configured for driving the first lens or the second lens to move for many times and calculating contrast values of the first image or the second image captured after each of movements when the repeated pattern detection module judges that the repeated pattern appears, and controlling the first lens driving module and the second lens driving module to drive movements of the first lens and the second lens for focusing according to the calculated contrast values.