Dust cake compressibility of fine fly ashes on a filter system was carefully investigated under well-controlled conditions and by measuring the cake thickness under different filtration conditions using an on-line powder pressure-displacement measurement system. Cake thickness, collection efficiency, and pressure drop of dust cake were investigated at the different filtration superficial velocities of 10cm/s, 15 cm/s, 20 cm/s, 25 cm/s, 30 cm/s. 35 cm/s and 40cm/s, and dust concentrations of 200g/m(3). The compression stress had also been found to increase with the increasing filtration superficial velocity. The results showed that the cake porosity decreased and the specific cake resistance and the collection efficiency increased with the enhancement of compression stress. The test results of this study can be applied in different system of filters during cross-flow filtration. (C) 2009 Elsevier B.V. All rights reserved.