Numerical simulation was carried out in the present paper to demonstrate the effect of the pitch-angle scattering on the phase space distribution of the proton fluxes measured in the Earth magnetosphere. It was shown that for Mc' Ilvine parameter of order 2-4 even a small order of magnitude of the pitch-angle diffusion coefficient may essentially affect the phase space distribution of the radiation belt proton fluxes. Numerical simulations carried out demonstrate that for future predictions on the satellite measurements it is expedient to obtain the reliable theoretical pitch-angle quasilinear diffusion coefficients with the appropriate experimental verification.