The mechanism of cake formation in constant pressure filtration of power law slurry is studied, By analyzing the forces exerted on the depositing particles, the critial friction angles, theta(c), are estimated under various conditions, The lowest value of theta(c) is found when the frictional drag and the interparticle force are of the same order of magnitude, The packing structure of particles on the cake surface has been simulated, and the results indicate that a more compact cake will be obtaind if a power law slurry with smaller n is filtered, A numerical program besed upon the continuity equation and the Rabinowitsch.Mooney equation is also designed to estimate the variations of local cake properties during a course of constant pressure filtration, The calculated results of cake porosity and specific filration resistance agree very well with the experimental data.