The electonic structure and optical properties of standard InGaAs material, which formed the absorption layer of transferred-electron InP/InGaAs photocathode, were studied based on the density functional theory, the exchange and correlation potential energy was described by Heyd-Scuseria-Ernzerh(HSE06). First, the energy band structure of zinc blende GaAs was verified with this hybrid density functional, then the standard InGaAs bulk model was established, and dynamically optimized by self-consistent method before complex dielectric function was obtained, then the optical absorption coefficient was derivated from Kramers-Kronig relation. Finally, under the estimation of P-type standard InGaAs unequilibrium minority carriers effusion length were 0.8, 1.0, 1.2, 1.4, 1.6 and 2.0 m separately, combined with quantum efficiency formula of transferred-electron photocathode, the optimized absorption layer thickness of InP/InGaAs photocathode was derivated according to the photon energy between 0.780 260 eV and 0.820 273 eV with spacing 0.002 eV.