With the development of society and energy crisis, searching for new energy materials and developing new energy have been one of the eternal subjects. In addition to natural energy materials and new energy materials, such as solar cell, Li-ion battery, thermoelectric conversion materials, etc., nanogenerator is also a hot spot which is based upon a certain nana-material and nano-effect. The most famous nanogenerators are the piezoelectric nanogenerator which is based on piezoelectric effect of ZnO nanorods in 2006, and triboelectric nanogenerator which is based upon the triboelectrification and electrostatic induction effects. Up to now, these two kinds of nanogenerators are closer to practical applications. In recent years, several researches have revealed that under certain conditions, graphene exhibited an ability for energy conversion and harvesting. For example, flow of a liquid, gas flow, acoustic and cyclical force, etc. In our research, monolayer graphene sheets were deposited on a transparent and flexible polydimethylsiloxane (PDMS) substrate, and a tensile strain was loaded by stretching the substrate in one direction. It was found that an electric potential difference between stretched and static monolayer graphene sheets reached 8 mV when the strain was 5%. Theoretical calculations for the band structure and total energy revealed an alternative way to experimentally tune the band gap of monolayer graphene, and induce the generation of electricity. Comparing with other nanogenerators, the graphene-based nanogenerator provides advantages, such as simple assemble, flexibility and high structural stability. It is expected this nanogenerator is of potential applications in active sensors and sustainable power source.