The invention relates to a high-temperature corrosion inhibitor for an H2S-HCl-H2O system and a preparation method of the high-temperature corrosion inhibitor. According to the preparation method, methyl-alpha-naphthyl ketone, morpholine and sulfur are taken as main raw materials and are subjected to a Willgerodt-Kindler method to generate naphthylethyl thioacylmorpholine. The high-temperature corrosion inhibitor comprises the following components in percentage by weight: 30%-50% of ethyl thioacylmorpholine, 5%-15% of hexadecyl pyridine, 10%-15% of alcohol amine compounds, 1%-3% of potassium molybdate or potassium tungstate and 29%-57% of a solvent. The high-temperature corrosion inhibitor belongs to strong-adsorption mixed type corrosion inhibitors, is capable of forming a layer of compact protecting film on the surface of metal and particularly applicable to the corrosion prevention of the H2S-HCl-H2O system and can be generalized and used for the prevention of sulfuretted hydrogen corrosion in the industries of oil fields, boilers and steel mills. The use temperature of the high-temperature corrosion inhibitor during the use can reach 120 DEG C; the high-temperature corrosion inhibitor has the characteristics of low consumption, high efficiency, wide use temperature range, good dispersity and low environmental pollution and is simple and convenient to produce.