In the modeling of complex initial permeability of polycrystalline ferrites the definite sample is characterized with its microstructure: the average grain size and log-normal distribution of sizes. Grains are assumed as statistically independent objects in the averaging process of their magnetic characteristics (that for current size grain is assigned on the analogy with ones of actual samples). Distribution of resonators – oscillating domain walls in grains naturally explains resonance or relaxation character of spectrum (as a particular inhomogeneous spectral broadening) but statistical averaging of permeability of grains results in analytic relation for frequency dependence of absorption component of permeability, unveiling the main effects of microstructure.