Graphene oxide (GO) has aroused worldwide interests in recent years because of perfect solubility, easy processing nature, and intriguing mechanical properties. However, safety risk, high pollution, and low synthesis rate involved in the synthesis process of GO limit its practical applications. In this work, we propose a new strategy to efficiently produce the high-quality GO based on microfluidic synthesis technology. By use of the H2SO4/H3PO4/graphite hybrid microdroplet as the microreactor, the exfoliation and oxidation of graphite can be confined in a microscale reaction environment, indicating the enhanced reaction kinetics, high reaction rate (reaction time of 2 h), and minimum safety risk. Notably, the microfluidic synthesis of GO has nearly the same chemical structure when compared with the Hummers method. More importantly, the rGO fibers processed from GO solutions possess a high specific capacitance of 716.2 mF cm(-2) (23.86 F g(-1)) and an energy density of 14.5 mu Wh cm(-2) (0.53 Wh kg(-1)), which can enduringly power a smart watch. These versatile strategies open a promising access to the fast synthesis and commercial applications of graphene.