1. A 3D image processing method for use in an electronic device having an image decoding unit with a sequence of decoding sub-units, wherein the method comprising: receiving at least one 3D image by a first decoding sub-unit; decomposing the 3D image into a left image or a right image according to a 3D format corresponding to the 3D image by a second decoding sub-unit; and performing a control operation according to the left image or the right image by a third decoding sub-unit, wherein the third decoding sub-unit is in the rear of the second decoding sub-unit in the sequence; wherein the second decoding sub-unit further puts a tag of image type into a specific position of data corresponding to the left image or the right image, in which the tag of image type comprises a tag of left image and a tag of right image.