Based on the Maxwell-Garnett effective medium theory,a novel theoretical model for investigating the optical properties of discontinuous metal nanofilm i s developed,and the corrections for both the volume fraction of hemispherical nanoparticles and the nano-size effect are proposed.On the basis of the mode l,the variations of effective relative permittivity and optical constant of the Au nan oparticles equivalent film with wavelength in the visible light region are given,and the sp ectra of reflectivity,transmissivity and absorptivity of nanofilm with nano-siz e effect are obtained.The computational results show that with increase of nano -size,both the effective permittivity and the optical constant increase with a slight red shift of the spectral peaks.It is further found that the smaller the film nano-size is,th e smaller the reflectivity and the absorptivity are,while the larger the transmissivity is,a nd there is a slight red shift of the peak positions with the nano-size increases.These resu lts agree with the experimental results.