A simple model is suggested for a qualitative analysis of spin-dependent (e,2e) reaction on a ferromagnetic surface. The model is based on the scattering of the primary electron with the average spin projection by the valence electron with the average spin projection . To test the model the energy distributions of correlated electron pairs are measured for parallel and anti-parallel orientations of the magnetic moment of the cobalt film and polarization vector of the incident beam. The proposed model explains qualitatively the spin-asymmetry of the measured binding energy spectrum.