The vanadium flow battery (VFB) as one kind of energy storage technique that has enormous impact on the stabilization and smooth output of renewable energy. Key materials like membranes, electrode, and electrolytes will finally determine the performance of VFBs. In this Perspective, we report on the current understanding of VFBs from materials to stacks, describing the factors that affect materials' performance from microstructures to the mechanism and new materials development. Moreover, new models for VFB stacks as well as structural design will be summarized as well. Finally, the challenges, the overall cost evaluation, and future research directions will be briefly proposed.