Abstract: The physical properies and chemical composition of the high-level radioactive sludge(HLRS) and HLLW on the different height of the HLLW storage tank have been studied. The HLLW comes from military reactor fuel. HLRS mainly consists of BaSO_4, K_3PO_4·6MoO_3, nitrate crystals and (amorphous) silicate. The formation mechanism and dissolving method of the sludge are discussed. The results obtained from this work are very important for the sludge treament and disposal.