In this work, an ether-based electrolyte is adopted instead of conventional ester-based electrolyte for an Sb2O3-based anode and its enhancement mechanism is unveiled for K-ion storage. The anode is fabricated by anchoring Sb2O3 onto reduced graphene oxide (Sb2O3-RGO) and it exhibits better electrochemical performance using an ether-based electrolyte than that using a conventional ester-based electrolyte. By optimizing the concentration of the electrolyte, the Sb2O3-RGO composite delivers a reversible specific capacity of 309 mAh g(-1) after 100 cycles at 100 mA g(-1). A high specific capacity of 201 mAh g(-1) still remains after 3300 cycles (111 days) at 500 mA g(-1) with almost no decay, exhibiting a longer cycle life compared with other metallic oxides. In order to further reveal the intrinsic mechanism, the energy changes for K atom migrating from surface into the sublayer of Sb2O3 are explored by density functional theory calculations. According to the result, the battery using the ether-based electrolyte exhibits a lower energy change and migration barrier than those using other electrolytes for K-ion, which is helpful to improve the K-ion storage performance. It is believed that the work can provide deep understanding and new insight to enhance electrochemical performance using ether-based electrolytes for KIBs.