The invention relates to a positive and negative electrode electrolyte and a preparation method and application thereof in an A12 type flow battery, belongs to the field of electrochemistry, and is widely applied to large-scale energy storage of new energy. An active substance of the negative electrode electrolyte in the A12 type flow battery is K3Fe(CN)6, wherein the constant pH value is maintained through hexamethylenetetramine-hydrochloric acid; an active substance of the positive electrode electrolyte is Fe(6, 6'-dmbpy)3Cl2, wherein a constant pH value is maintained through glycine-hydrochloric acid; the anode and cathode solid energy storage substances are Prussian blue Fe4[Fe(CN)6]3; the transfer of electrons/charges between the positive and negative electrodes and the solid energy storage material Fe4[Fe(CN)6]3 is achieved through the oxidation reduction of intermediates K3Fe(CN)6 with Fe(6, 6'-dmbpy)3Cl2. The energy density can reach more than two times of that of the existingall-vanadium redox flow battery, but the cost of the active materials is only one tenth of that of the existing all-vanadium redox flow battery.