Blend membranes of quaternized polysulfone/polyvinylidene fluoride (Q/P) for all vanadium redox flow battery (VRFB) are prepared by one-step solution casting method to reduce the vanadium permeation and improve the mechanical properties of pure quaternized polysulfone membrane. The physicochemical properties and electrochemical performances of the Q/P membranes are characterized in detail. In comparison with the Nafion 115 membrane, Q/P blend membranes exhibit higher water uptake, ion exchange capacity (IEC) and swelling ratio, lower ionic conductivity and ultra-lower vanadium permeability, better stability and superior VRFB cycle performances. Owing to the ultra-low vanadium permeability, the VRFB with Q/P-20% blend membrane has shown the highest coulombic efficiency of 99.29% at 80 mA cm(-2) and the Q/P-15% membrane has shown the highest EE of 91.12% at 40 mA cm(-2), which is 4.89% and 3.33% higher than that of Nafion 115 at the same current density, respectively. The mechanical properties of the Q/P blend membranes increase with the increasing of the PVDF mass ratio. It reveals that the introduction of PVDF is of great significance to improve the performances of the Q/P blend membranes.