The galactic cosmic ray (GCR) particle flux model has been developed by using the experimental data obtained during the solar cycles 21–24. The model calculates fluxes of GCR particles (with charge z from 1 to 28 and energy E from 80 up to 105 MeV/nucleon) in the interplanetary space (ecliptic plane) as a function of solar activity (sunspot number) and the heliocentric distance. GCR proton fluxes computed by the model for the case of a possible decrease in solar activity during solar cycles 25 and 26 are discussed. Key Points The GCR particle flux model is developed by using a wide range of experimental data obtained during the 21–24 solar cycles GCR proton fluxes in interplanetary space depending on calendar time are calculated and discussed for 25th and 26th predicted solar cycles This forecast indicates a continuing trend of solar activity reduction starting since the 23rd solar cycle