The invention relates to mixed ionic liquid formula solution, which consists of an ionic liquid A, an ionic liquid B and a mixed solvent C, wherein the positive ion of the ionic liquid A is the N,N-dialkyl imidazole positive ion or the N,N,N,N-tetra alkyl quaternary amine positive ion, while the negative ion thereof is the monobasic carboxylic negative ion; the positive ion of the ionic liquid B is the protonated alkylamine positive ion, while the negative ion thereof is the monobasic or binary or ternary carboxylic negative ion; and the mixed solvent C is aqueous solution of water, polyethylene glycol, polyglycol ether, propylene carbonate or tetramethylene sulfone. The mixed ionic liquid formula solution of the invention is strong base-weak acid and weak base-weak acid mixed salt solution, has wide pH buffering capacity, and can greenly efficiently absorb the SO2 gas in a reversible cycle mode. The mixed ionic liquid formula solution of the invention is adopted as a SO2 absorbent so that the requirement for the equipment required by SO2 absorption is simple, the operation condition of absorbing and desorbing SO2 is mild, the desulfurization efficiency is high, and the problems of waste solution and wastewater discharge and the like do not exist. The invention also discloses a preparation method for the mixed ionic liquid formula solution.