The invention relates to a metallographical corrodent and application of the metallographical corrodent in displaying carbide and grain boundaries in rolled steel and belongs to the technical field of chemical etching of metal materials. The metallographical corrodent is prepared from picric acid, a surfactant A, a surfactant B and the following raw materials, by volume, 3-5 parts of acetic anhydride, 60-75 parts of methyl alcohol and 20-40 parts of water, wherein 0.2-0.4 g of the picric acid is correspondingly adopted for each 1 ml of the methyl alcohol; the surfactant A is sodium dodecyl benzene sulfonate; the surfactant B is at least one of fatty alcohol-polyoxyethylene ether sodium sulfate, dodecyl alcohol amide and nonylphenol polyoxyethylene ether; and the mass ratio of the picric acid to the surfactant A to the surfactant B is (1-8): (3-6): (0.2-0.5). By means of the metallographical corrodent, rapid, clear and true displaying of the carbide and the grain boundaries in the rolled steel can be achieved.