Using DET-GGA-PW91 calculations we investigate the electronic structures and optical properties of doped GaP. It is found that the lattice constants and volume increase slightly for Al, In, As and Sb doped systems and E-G distinctly decrease after doping. The formation energies are 0.587 and 0.273 eV for As and Sb doped systems, respectively, and lower remarkably than those in other systems, indicating that the stability of the two systems is higher. The direct band gap transition occurs when doped with In, As and Sb elements. The charge density difference images reveal that electron loss near Al atom is observed accompanying the enhancement of covalent bond feature, and then electron enrichment is present around N atom demonstrating that the ionic bond characteristic is obvious. The Sb-doped system has the higher static dielectric constant illustrating the applications in semiconductor devices. The absorption peak value is located at 194.7 nm for Al-doped system and this shows that the system can absorb a large amount of light and displays "Barrier-type" characteristics in UV region. In the visible region, the doped systems have lower reflectivity coefficient, indicating that the systems all have "clear-type" properties. This is conducive to fundamentally insights to a tunable band gap semiconductor with enormous potential in device fields. (C) 2017 Elsevier B.V. All rights reserved.