The invention discloses a depth estimation method based on an image definition difference. The method comprises steps of converting a color single-viewpoint single image into a gray-scale image, conducting partitioning, calculating definition of all image blocks by selecting an image definition algorithm, regarding the definition of all image blocks as definition of pixels of all image blocks and obtaining the definition difference condition of the single-viewpoint single image. Under the actual condition that a camera focuses on a foreground of a scenery target usually so that the focused scenery is clear, the depth assignment is conducted to the single-viewpoint single image through the definition difference, a depth image is obtained, and the depth estimation of the single-viewpoint single image is completed. The definition is calculated in partitioning, and the single-viewpoint single image depth is obtained. Compared with the prior art, the method has the advantages of being low in complexity and capable of meeting real-time requirements of image processing.