To favor the control of membrane fouling on line by relaxation and backwash sequencing, two major fouling origins are considered: the former is due to retention of large particles on the membrane surface forming a growing deposit that can be controlled by tangential shear stresses, the second is due to the retention of the largest soluble polymers forming a thin layer on the membrane surface including pore blocking and inducing a progressive reduction of the deposit porosity, the influence of this second fouling origin can only be reduced by backwashing. A simple model was developed to represent (i) the accumulation of two types of compounds and its consequences and the evolution with time of the hydraulic resistance of the system and (ii) the role of relaxation and backwashing to reduce the fouling impact. Some simulations were presented according to the values of the three model parameters. Simulations were also compared to experimental data obtained on biological suspensions.