Based on the first principles study， this paper investigates the control of the optical properties of GaN（0001） surface by metal atoms. The work was conducted with different kinds of metals （Ni， Ru， and Au） that are commonly used in experiments. The results show that charge transfer occurs from adatoms to GaN（0001） surface，and the work function of GaN（0001） surface is reduced by Ni and Ru adsorption. The impurity energy levels are introduced to the band gap of GaN（0001） surface， resulting in the reduction of barrier height of carrier transition， the optical properties are then modulated. The red shift of main peaks in the low photon energy region for all the optical parameters and the shrinkage phenomenon of all the optical curves in the high photon energy region are observed， the numbers and positions of characteristic peaks in all the optical curves change significantly. Furthermore， the absorption of GaN（0001） surface to visible light and even infrared light is enhanced after the adsorption of metal atoms， which is suitable for the longer wave light detection instead of UV detection.