Abstract: The differences and relations between sharpness broadening of penumbral imaging system and full width at half maximum (FWHM) of general system’s point spread function （PSF）were illuminated and the concept of sharpness broadening of penumbral imaging system was determined. The penumbral encoding pinhole imaging system Monte-Carlo model was built; the system PSFs of γ ray and neutrons in energy of 0.662, 1.25, 2.45, 5.0, 10.0, 14.06 MeV and so on were calculated respectively. The function of the PSFs sharpness broadenings vs γ ray and neutron energy was obtained and the broadening reasons of the system sharpness were analyzed in detail, the theoretical reference was presented for the future design improvement of encoding pinhole.