This study reports the preparation of iridium-decorated graphene (Ir-G) as an electrode material for an all-vanadium redox flow battery (VRB) by synchronously reducing graphite oxide (GO) and iridium chloride hydrate (IrCl3·3H2O). X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution X-ray photoelectron spectroscopy (XPS) were employed to characterize the physicochemical properties of Ir-G. Cyclic voltammetry (CV) was used to measure the electrochemical behaviors of the Ir-G for the VRB system. In addition, this study investigated and compared the electrochemical behaviors of graphene with those of Vulcan XC-72. The Ir nanoparticles were exclusively deposited on graphene surface with high uniformity and a mean size of 3nm. The CV results reveal that Ir-G possesses a highly electrocatalytic activity and reversibility among all samples. In addition, the redox current densities of Ir-G are approximately four times higher than those of XC-72. The large electrolyte-accessible surface area and intense affinity of Ir/vanadium-oxygen ions that facilitate electronic and ionic transport contribute to these improvements. Therefore, this study proposes a synchronous reduction method for preparing an Ir-G electrode that exhibits excellent electrocatalytic performance, thereby demonstrating significant improvements in VRB applications.