1. A dead pixel detection method for image applicable in a digital camera, comprising at least the following steps: obtaining an image from outside through said digital camera; and selecting sequentially a pixel-to-be-tested from said image and an adjacent pixel group when there are pixels in said image that have not yet been detected, and executing the following steps: searching and obtaining out a first pixel and a second pixel in said adjacent pixel group for calculating a gray level value difference; calculating an average gray level value of the pixels in said adjacent pixel group other than said first pixel and said second pixel; designating the sum of said average gray level value and said gray level value difference as an upper gray level threshold, and the difference of said average gray level value and said gray level value difference as a lower gray level threshold; and when the gray level value of said pixel-to-be-tested is outside the range of said upper gray level threshold and said lower gray level threshold, designating said pixel-to-be-tested as a dead pixel.