The invention discloses an all-vanadium flow battery. Flow frame plates are provided with liquid inlet holes and liquid outlet holes; the front faces of the flow frame plates are provided with liquid inlet branch flow channels and liquid outlet branch flow channels; the flow frame plates are arranged in sequence sequentially and alternatively in a front face to front face and back face to back face way; an ion exchange membrane is clamped between the front faces of adjacent flow frame plates; a current-conducting plate is clamped between opposite back faces of adjacent flow frame plates; electrodes are arranged in inner frames of the flow frame plates; the aspect ratios of the electrodes are 3-15; the heights of the electrodes are 1-25 centimeters; and the widths of the electrodes are less than or equal to 200 centimeters. In the all-vanadium flow battery, electrodes of large aspect ratios, small heights and large widths are adopted. The all-vanadium flow battery has the advantages of simple structure, small quantity of assemblies, small thickness, small size, low internal resistance, easiness in processing, convenience in assembling, good mass transfer effect and low diffusion polarization of vanadium electrolytes inside the electrodes, low self-discharge current, high power density, high vanadium utilization ratio, high energy efficiency, low cost and high benefit.