We present a first-principles investigation of the electronic structure for Cu2HgGeS4 in stannite structure using the screened-exchange density functional method. This crystal is a direct-band-gap semiconductor, and the calculated band gap is 1.27 eV. The dielectric function, absorption coefficient, reflectivity, and energy-loss function in the two independent polarizations are also studied using the density functional theory (DFT) within the screened-exchange local density approximation (sX-LDA). We discuss the high-frequency dielectric constant and optical transitions between the valence bands (VBs) and the conduction bands (CBs) in the spectra of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption spectrum for this material. The prominent structures in the spectra of reflectivity and energy-loss function are discussed in detail. The anisotropy is reflected in all the optical spectra.