Graphene has stimulated enormous interest due to its intriguing structure and fascinating properties. The extremely high carrier mobility, mechanical flexibility, and optical transparency as well as the versatility for band structure engineering make graphene a promising candidate for next-generation carbon-based electronic devices. Graphene chemistry, the covalent functionalization of graphene as a 2D giant molecule, offers a promising direction to controllably tailor its properties through the introduction of various chemical decorations. One of the great challenges for graphene functionalization originates from its strong chemical stability, thus highly reactive chemical species are needed as the reactants. In recent years, novel photochemical approaches have been developed to achieve efficient graphene modification and bandgap modulation, following a general concept of “Photochemical Bandgap Engineering of Graphene”. In this article, such kinds of photochemical graphene engineering are demonstrated, together with a brief discussion on the future directions, challenges, and opportunities in this fascinating research area.