The invention discloses a dendritic crystal corrosion macroscopic examination reagent for solidification structures and defects of a continuous cast blank and a preparation method thereof. The reagent comprises the following components by mass percent: 0.28-1.09% of copper chloride, 0.17-0.27% of magnesium chloride, 0.56-1.60% of ferric chloride, 1.28-1.30% of hydrochloric acid with the mass concentration of 36-38%, 54.70-55.80% of absolute ethyl alcohol and the balance of water. The preparation method comprises the following steps: adding the water into a container, and then adding the copper chloride, magnesium chloride, ferric chloride and hydrochloric acid; and adding the absolute ethyl alcohol after all the added raw materials are fully dissolved, and evenly stirring. Compared with the prior art, the invention solves the problem that other corrosive reagents can not clearly display the dendritic crystal solidification structures of a continuous cast blank; and the reagent has thecharacteristic of original-size display without expansion or reduction for interior defects of a continuous cast blank when used for dendritic crystal corrosion macroscopic examination on the solidification structures and defects of the continuous cast blank.