The invention discloses a preparation method and application of a low toxicity acidizing corrosion inhibitor. The preparation method mainly includes two steps: 1. synthesizing a Mannich base quaternary ammonium salt; and 2. diluting the Mannich base quaternary ammonium salt to 15-20% (mass percentage) with a solvent. The corrosion inhibitor disclosed in the invention is a typical adsorption type corrosion inhibitor, can rapidly form a compact and firm hydrophobic protective membrane on the surface of a P110 steel test piece, thus effectively preventing an acid solution from corroding P110 steel. The corrosion inhibitor prepared in the invention belongs to a mixed corrosion inhibit inhibitor. The inhibitor employs cinnamic aldehyde with the advantages of the green, low toxicity, easy degradation and the like to replace the cancerogenic substance formaldehyde, is not added with iodide, alkynol or other synergists polluting the environment, has the advantages of simple synthesis process, small dosage, low toxicity, etc., and is suitable to oil and gas well acidizing, acid fracturing stimulation and other operations.