The optical properties of Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystal near morphotropic phase boundary were investigated by temperature dependent transmittance and reflectance spectra. The temperature dependent absorption edges show blueshifts below 300 K while they show redshifts above 300 K. At 303 K, optical band gap Eg is 3.25 eV, critical point energies Ea and Eb are 3.93 and 4.65 eV, respectively. With increasing temperature, Eg, Ea and Eb decrease and they are 3.05, 3.57, 4.56 eV at 453 K, respectively. Three critical point energies Eg,Ea and Eb are corresponding to O 2p to Ti d, and Pb 6p, respectively. Such narrowing trends with increasing temperature can be explained by thermal expansion of the lattice and electron-phonon interaction. Based on Tauc-Lorentz dispersion models, the dielectric functions from 3.1 to 6.5 eV have been extracted from303 to 453 K. It was found that the refractive index n increases with increasing temperature.