The filtration tests were made in cell with a low concentrated suspension. The suspension with a concentration of cM=1.14～2.67․10-3 g/g consists of paper paint and water. The particles in the suspension have a particle size x<1㎛. The used depth filters consists of glass fibres, which are coated by polymer. The filtration in depth filters accorded in different mechanism, which were explained by physical models. The model which would be allows to make a promise of the filtration reaction. This filter media allows to get a high filtration time and a good separation rate. The Particle distribution is measured by a photon correlation spectroscopy(PCS). PCS measures particle sizes 0.03 ㎛<d<3 ㎛ in the suspension. The filtered suspension has a very low concentration Co≤5×10-4 g/g of solid in sample. The PCS also informs us about the number of the particles in the suspension. The makes it possible to calculate the concentration of the in sample.