This paper is mainly devoted to the refinement of the crystal unit cell parameters of the native manganese oxide from the supergene oxidation zone of the Xiangtan manganese deposit, Hunan Province. With the computer programs of Rietveld_DBW 9411 and Pirum, it is revealed that the body_centered monoclinic cryptomelane is the main phase of the mineral. It is for the first time to give the unit cell parameters of native cryptomlane in this area:a0=0.997 4 nm,b0=0.286 3 nm,c0=0.969 3 nm,β=91.467°,V =276.66×10-3nm3. It is also pointed out that the troubles of refining are caused by the extreme difficulty in finding a single crystal particle and by the XRD pattern characterized by broadening, relatively high background and asymmetry.