The electronic and optical properties of the cubic zinc-blende (ZB) structured filled tetrahedral semiconductor α-LiZnN under pressure are investigated by using ab initio plane wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The electronic band structure and the density of state under pressure are systematically described. The basic optical constants, including the reflection and absorption spectra, the energy-loss function, the complex refractive index and the dielectric function, are calculated and analysed at different exteal pressures. Our results suggested that the ZB α-LiZnN is transparent in the partially ultra-violet to the visible light region, and it seems that the transparency is hardly affected by the pressure.