Strain engineering usually refers to a kind of material processing technology which aims to regulate the properties of materials or optimize related devices' performance by inherent or external strain. In recent years, with the development of 2-D materials, the research surrounding strain engineering of 2-D materials (transition metal dichalcogenides [TMDCs], graphene, etc.) has attracted significant attention. Compared with strain engineering of traditional bulk materials, the atomic thickness of 2-D materials makes them more suitable to serve as the platform for strain-engineering research and builds a bridge between strain engineering and nanophotonics. Hence, they are worthy of attention from many points of view, from fundamental physics to practical applications.