A mathematical model has been developed to provide insight into hydraulic behaviour of the rnicrostraining process. The model employs the clasic laws of particle bed hydraulics to predict the varying hydraulic resistance of the cake as it is developed on the inside surface of the fabric ( drum ). The model is developed on the basis that flow rate through any section of a microstraining medium and the resultant headloss can be predicated with the Carman Kozeny relationship for flow through a porous medium. The micro-straining drum is segmented throughout the sub-merged portion and each segment is analyzed individually using polar co-ordinates, to reduce the problem to a steady-state analysis. The proposed formulation for hydraulic resistance of clean fabric and the cake together with the particle routing can be used to predict the liquid throghout and solids removed efficiency of the microstrainer.