The invention discloses an aqueous-solution sodium-ion battery, and a cathode material, a preparation method and an application of the battery. The cathode material is a manganese oxide-containing material used for a cathode active material of the aqueous-solution sodium-ion battery and has the chemical general formula of NaMn<1-y-z>ATiO<2-delta>, wherein A is a doped element and specifically is one or more selected from B3+, Al3+, Cr3+, Mn4+, Fe3+, V3+, and Mo6+; and x, y, z, and delta satisfy relationships of 0<=1-y-z<=x, 0<=z<1-x, and x+3(1-y-z)+ay+4z=2(2-delta), wherein 0.55<=x<=0.8, -0.02<=delta<=0.02, and a is the valence of the doped element A.