Spectroscopic ellipsometry was used to investigate the optical properties of Mn film deposited with different sputtering pressures on silicon substrates in the photo energy range of 2.0~4.0eV. Parameterized analyses, based on Drude-Lorenz model and Bruggeman effective-medium approximation model, were used to fitting the elliptic parameters. The results imply that the density of Mn films first increases and then decreases with increasing of Ar pressure, whereas the refractive index changes with Ar pressure in a contrary way. Meanwhile, the extinction coefficient has a complex relationship with Ar pressure at lower photo energy, the extinction coefficient changes in line with the refractive index when photo energy exceeds 2.8eV. Moreover, the effects of Ar pressure on optical constant of the film depend strongly on the variation of the Mn atomic density.