A fast focusing method for a digital camera is applied in an auto focusing stage for judging whether the digital camera needs to be refocused. The fast focusing method includes recording a system time after a previous focusing (defined as a first time); capturing a system time before a current focusing (defined as a second time); performing a fuzziness detection procedure to acquire a focus value when a difference obtained by subtracting the first time from the second time is greater than a focusing time threshold; setting a focusing focal length range covering a reference focal length when the focus value is between a lower limit focusing threshold and an upper limit focusing threshold; capturing images at different focusing focal lengths respectively in the focusing focal length range; calculating a contrast value of each image; calculating a target focal length from the contrast values through a quadratic curve approximation method.