The invention discloses an etching agent and a display method for displaying a medium-carbon manganese-containing steel continuous casting billet solidification structure. The display method comprises: (1) taking a medium-carbon manganese-containing steel continuous casting billet sample, and polishing; (2) uniformly mixing 40-60% by volume of a sodium metabisulfite saturated aqueous solution and 40-60% by volume of a picric acid saturated alcohol solution, and placing for 0.5-2 h; and (3) downwardly placing the testing surface of the polished sample in an etching agent until the solidification structure of the testing surface is clearly displayed. According to the present invention, the etching preparation is simple, the operability of the etching process is strong, hot acid etching is not required, the environmental pollution is low, the etching effect is good, and the dendritic crystal structure of the etched sample can be clearly observed after the polishing so as to provide the condition for the detection of the component between the dendritic crystal arm and the dendritic crystal; and the solidification structures of the etched sample is clearly displayed, the good effects are provided under SEM and EPMA, and the favorable conditions are provided for the detection of the component between the dendritic crystal arm and the dendritic crystal.