This research is based on experimental results of magnetization and magnetic susceptibility of ferrite slab prepared in a previous work with a computerized simulation to find the influence of ferrite slab on a microwave propagation in terms of determining the behavior of attenuation factor .A slab of ferrite Co0.6Zn0.4Fe2O4were prepared by classical ceramic method. We have studied an influence of slab of the CoZn-ferrite its thickness is , loaded in a rectangular waveguide on a propagation of microwaves. The values of the reverse and forward attenuation factor has been found. After that, we choose the location of the slab X0 inside the guide which means the optimum status of microwave propagation has been reached at .