The evolution of electronic structures of hydrogenated graphene with different amount of hydrogen (H) coverage was investigated by ultraviolet photoemission spectroscopy and optical absorption spectroscopy. Raman spectroscopy and x-ray photoelectron spectroscopy were used to monitor and evaluate the H coverage. At low H coverage, the sp³ C  H bonds embedded within a sp² C matrix behave as defects in graphene and depress the delocalized π electron system. At high H coverage, two localized π electron states originating from the sp² C clusters encircled by the sp³ C  H matrix appear in the electronic band structures, and an opening of a band gap has been observed.