A theoretical model to predict the porosity and specific resistance of cake layer was developed for better understanding a coagulation-microfiltration system for drinking water production. The model was based on fractal theory and incorporated intra-floc and inter-floc porosities as well as cake collapse effect. The cake porosity was also determined experimentally using a confocal laser scanning microscope (CLSM) and image analysis to verify the validity of the model. Using the model, specific cake resistances can be simulated as a function of floc size and fractal dimension. The specific cake resistance decreases upon increasing the floc size and decreasing the fractal dimension.