The spectral features of Kerr rotation and ellipticity of MnBi film have been found to greatly change with temperature from 85 to 475 K, and the Kerr rotation at 700 nm increases over 50%. And the complex refractive index at room temperature and the dielectric and conductivity tensors at 85, 300, and 475 K have been determined with the reflectance of an opaque film, the transmittance of a semitransparent film and the Kerr effect. There are two distinct peaks in the \ensuremath{\omega}${\mathrm{\ensuremath{\sigma}}}_{\mathit{xy}}^{\mathrm{\ensuremath{''}}}$ spectrum, corresponding well to that of Kerr rotation. By comparing those results with the reported calculations, it becomes clear that the Kerr rotations originate principally from the interband transitions of Mn 3d\ensuremath{\downarrow} electrons (\ensuremath{\Elzxh}\ensuremath{\omega}2.5 eV) and of Mn 3d\ensuremath{\uparrow} electrons (\ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\gtrsim}2.5 eV). And the changes of the exchange splitting and the spin-orbit interaction strength are responsible for the strong temperature dependence of Kerr effect. Specific Faraday spectra at different temperatures have also been calculated with the above optical and dielectric constants and are much different from the reported data. \textcopyright{} 1996 The American Physical Society.