The invention provides a preparation method of a lansoprazole intermediate. The preparation method comprises the following steps of: mixing trifluoroethanol with 2, 3-dimethyl-4-chloropyridine-N-oxide and inorganic alkali compounds, and conducting reflux reaction to obtain 2, 3-dimethy-4-trifluoroethyoxyl-pyridine-N-oxide. Since the 2, 3-dimethyl-4-chloropyridine-N-oxide is used as raw materials, the trifluoroethanol not only is used as a reaction raw material, but also is used as a reaction solvent and other solvents are not needed to be introduced, the complex post-treatment of recovering the trifluoroethanol through fractionation is avoided and the step of post-reaction treatment is simplified; and since cheap and easy-to-obtain industrial alkali compounds such as potassium carbonate and potassium hydroxide are used, not only can the reaction be conducted smoothly and is the yield high, but also catalysts for catalysis are not needed, the step of complex catalyst recovery is not needed, the post-reaction treatment becomes simple, the degree of safety is high, the cost is lower and the yield is high.