The structural phase transformation under induced pressure of the GaAs- zinc blende (ZB) phase to rock salt (RS) phase, elastic properties and electronic structure of the stable (ZB) phase are studied under the framework of the density functional theory (DFT). When pressure is increased up to 10.7 GPa, transition from the GaAs-ZB to GaAs-RS structure occurs and the dependence of volume decrease of ZB to RS structure at the transition pressure is 14.11%. The elastic parameters such as elastic constants C11, C12, C33, Zener anisotropic factor (A), Kleinmann parameter (?), Poisson's ratio (?), Youngs modulus (Y) and energy band gap of GaAs-ZB structure shows a systematic variation with increase in pressure upto transition pressure. The results are found to be in consistent with other experimental and theoretical results.