The invention discloses an inhibiter for preventing metal from being corroded. The inhibiter is composed of 2-aminobenzothiazole and 2-phenylimidazoline. The problem that benzimidazole and derivatives thereof existing in the prior art are low in corrosion inhibition efficiency for carbon steel can be solved by the inhibitor. The inhibitor is composed of the 2-aminobenzothiazole and the 2-phenylimidazoline, when the weight ratio of the 2-aminobenzothiazole to the 2-phenylimidazoline is 0.78 : 1, the synergistic corrosion inhibition between the 2-aminobenzothiazole and the 2-phenylimidazoline can be played best, compared with a single inhibitor such as the 2-aminobenzothiazole and the 2-phenylimidazoline, the corrosion inhibition performance is enhanced greatly, and the corrosion inhibition efficiency of the carbon steel in an HCl solution can reach up to 89.8%.