The electronic and the optical properties of the cubic zinc-blende(ZB)BeS under high pressure have been in-vestigated by using ab inztio plane-wave pseudopotential density functional theory method in the generalised gradientapproximation(GGA)for exchange-correlation interaction.The electronic band structure and the pressure dependenceof the total and partial densities of state under pressure are successfully described.Our calculations show that the ZBBeS has large and indirect band gaps associated with(F→x)transitions in ambient conditions.The results obtainedare consistent with the experimental data available and other calculations.The optical properties,including dielectricfunction,energy-loss function,complex refractive index,reflection and absorption spectra,are investigated and analysedat different exteal pressures.The results suggest that the optical absorption appears moctly in the ultra-violet regionand the curve of refractive index shift toward high energies(blue shift)with pressure increasing.