Electrospun carbon fiber shows extensive application prospect in vanadium redox flow battery (VRFB) due to high electrical conductivity and large specific surface area. In this paper, in situ iridium (Ir) decoration by electrospinning technique was applied to further improve the performance of carbon fiber. In our work, Ir decorated carbon fiber (CF/Ir) composites with the diameter of about 200 nm was prepared via electrospinning technique and subsequent carbonization process. The morphology, composition, as well as electrochemical properties of CF/Ir have been systematically studied. CF-Ir-2 composite with proper Ir content showed excellent electrocatalytic activity towards VO2+/VO2+ redox reaction among all electrodes. Moreover, the cell performs well at charge-discharge measurements by employing CF-Ir-2 as positive electrode at the current density of 50-150 mA cm(-2). The discharge capacity of the cell using CF-Ir-2 can reach 79.5 mA h, increased by 43.1 mA h compared with that of the cell using CF, at the current density of 150 mA cm(-2). The corresponding energy efficiency for CF-Ir-2 is 12.2 % higher than that for CF. The superior electrocatalytic performance of CF/Ir composite was ascribed to the introduction of Ir as active sites and the strong connection between Ir and carbon fiber via electrospinning technique. In conclusion, Ir decorated carbon fiber as positive electrode shows excellent electrocatalytic properties for VRFB.