A hidden seam rehemming method for jeans, comprising steps as follows: (a) cutting down a part with desired length including the hem from the jean to be shortened, and cutting down the hem with a first seam allowance from the cut-down part; (b) taking out threads from the hem and unfolding the hem such that three rows of needle holes in the hem appear; (c) sewing the unfolded hem with a remaining part of the jean along the upmost row of needle holes in such way that the outside surface of the unfolded hem contacts the outside surface of the remaining part; (d). folding the first seam allowance of the hem and a second allowance of the remaining part toward the inside surface of the jean; (e). pressing the first and the second seam allowances with nail or iron such that the seam allowances lie against the inside surface of the jean; (f). folding the hem along original fold marks thereof such that the three rows of needle holes are superposed again and sewing it from the outside surface along the joint seam between the hem and the remaining part.