The lattice constant, the total energy, density of state, energy band structure, optical reflection and absorption properties of the zinc blende structure CdS under different pressure are calculated by using the generated gradient approximation (GGA) method based on density functional theory. Comparison of the electronic properties of CdS at high pressure with the energy band structural information indicates that a non-structural transition occurs at about 116.8 GPa, in which the direct band structure transforms to an indirect band structure. According to the electronic structure, the optical properties are analyzed systemically under different pressure.