The invention discloses a mannich base corrosion inhibitor for preventing CO2 corrosion in a high flow speed environment. The mannich base corrosion inhibitor is a compound which is prepared from the following components in percentage by weight: 30-40% of a main agent 2-dipropylene amino-methyl benzimidazole, 10-20% of benzyl alcohol, 5-10% of monoethanolamine, 5-7% of an emulsifier and 23-50% of a solvent, wherein a preparation method of the main agent comprises the following steps: 1) pouring benzimidazole and acetic acid into an enamel reaction kettle according to a mole ratio of 1:1, and uniformly mixing; 2) sequentially adding paraformaldehyde and dipropylene amino, uniformly stirring, heating to be 80-90 DEG C, and reacting for 12 hours, thereby obtaining 2-dipropylene amino-methyl benzimidazole, wherein the mole ratio of benzimidazole and paraformaldehyde to dipropylene amino is 1:1.5:1. The mannich base corrosion inhibitor has the advantages that no bad irritation odor is generated, the dosage small corrosion efficiency is high, the production is simple, rapid and convenient, good dispersion is achieved, an adsorption membrane is uniform and dense, and a material can be protected without spot corrosion or pitting corrosion.