Lithium-oxygen (Li-O2) batteries have attracted significant attention due to their ultra-high theoretical energy density, but are obstructed by the sluggish reaction kinetics at the cathode and high overpotential. Our previous researches have proved that energy fields such as light, force and heat are effective strategies to improve the reaction kinetics of Li-O2 batteries. Herein, we proposed a novel magnetic field-assisted Li-O2 batteries via a spin polarization strategy. By doping magnetic Mn2+ ions with spin polarization characteristics into CsPbBr3 (Mn-CsPbBr3) perovskite, a magnetic field-responsive cathode was designed and prepared. The incorporation of Mn2+ ions drives charge redistribution and spin polarization of CsPbBr3, which remarkably improve the carrier separation efficiency and the oxygen species adsorption energy. Increased spin-polarization of the magnetic elements by Zeeman effect in an external magnetic field results in the enhanced oxygen reduction and evolution reaction. In the magnetic field, a low overpotential of 0.40 V was obtained for Li-O2 batteries with Mn-CsPbBr3 cathodes which demonstrate an ultralow overpotential of 0.12 V and an ultra-high energy efficiency of 96.3% with the further illumination. The introduction of magnetic fields into the Li-O2 battery system and provides a new avenue for improving the reaction kinetics of rechargeable Li-O2 battery.