Graphene has potential applications in future microelectronics due to its novel electronic and mechanical properties. However, the lack of the bandgap in graphene poses a challenge and hinders its applications. In order to be able to work in ambient condition, gap engineering of graphene with nanostructure needs about sub-10 nm characteristic size, which increases the difficulty of fabrication and leads to less driving current that can be borne. In this paper, a new method to fabricate sub-10 nm graphene nanostructures is developed. With PMMA/Cr bilayer structure, sub-10 nm graphene nanostructures can be obtained precisely and repeatedly through controlling the etching time. Meanwhile, a new device based on graphene nanoconstrictions connected in parallel is designed and fabricated, whose band gap is bigger than that of graphene nanoribbon and whose characteristic width is the same as that of graphene nanoribbon. With the graphene nanoconstrictions connected in parallel, the band gap of the graphene can be adjusted effectively and the driving current can be significantly increased, which is very important for future practical applications of graphene.