In this article, a new dewatering device was designed to achieve high dry sewage sludge through proposing a new ultrahigh-pressure (UHP) technique with adding very few flocculant cationic polyacrylamide (CPAM). The design of the new dewatering device was based on the compression characteristic curve, which was obtained from the experiment on compression characteristics of sludge and the final moisture content. The mechanics and motion analysis were carried out for two key components, i.e. the toggle force amplifier and the disc spring. It showed that the compression ratio (C-r) of sludge between 40%-72% and the moisture content (We) of sludge cakes was below 50% with some sludge cake even below 20% by using 3 MPa pressure filtration. The moisture content of sludge was much lower than that of the routinely used device such as diaphragm frame filters. The force of the combination of toggle force amplifier and disc spring of the new device showed a 20-fold increase, and the dynamics property of the new device fits very well to the sludge compression characteristic curve. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.