The invention provides a Mannich base acidifying corrosion inhibitor and a preparation method thereof. The molecular general formula of the Mannich base acidifying corrosion inhibitor is as follows. The preparation method comprises the following steps: proportionally pouring dodecyl dimethyl tertiary amine, polyformaldehyde and aromatic ketone into a reaction kettle, adding an ethanol solvent, slowly adding hydrochloric acid to regulate the pH value of the reaction solution, heating to 80+ / -5 DEG C, and refluxing for 5-7 hours while keeping the temperature, thereby obtaining the Mannich base; and compounding the Mannich base, acetic acid, propiolic alcohol and potassium iodide in a weight ratio of 6:2.5:0.5:1 to obtain the finished Mannich base acidifying corrosion inhibitor product. The existing raw materials for synthesizing the Mannich base acidifying corrosion inhibitor are changed to enhance the adsorption strength and compactness of the corrosion inhibitor protective film, thereby enhancing the corrosion inhibition effect of the acidifying corrosion inhibitor and lowering the acidifying operation cost.