Alkaline zinc-based flow batteries are regarded to be among the best choices for electric energy storage. Nevertheless, application is challenged by the issue of zinc dendrite/accumulation. Here, we report a negatively charged nanoporous membrane for a dendrite-free alkaline zinc-based flow battery with long cycle life. Free of zinc dendrite/accumulation, stable performance is afforded for ∼240 cycles at current densities ranging from 80 to 160 mA cm⁻² using the negatively charged nanoporous membrane. Furthermore, 8 h and 7 h plating/stripping processes at 40 mA cm⁻² yield an average energy efficiency of 91.92% and an areal discharge capacity above 130 mAh cm⁻². A peak power density of 1056 mW cm⁻² is achieved at 1040 mA cm⁻². This study may provide an effective way to address the issue of zinc dendrite/accumulation for zinc-based batteries and accelerate the advancement of these batteries.