The preparation method of methylbenzotriazole is similar to BTA, and the classic method in industry is toluenediamine diazotization and cyclization in acetic acid to obtain BTA, and most manufacturers still adopt this synthetic route. The mixture of 2,3-methyl-o-phenylenediamine and 3,4-methyl-o-phenylenediamine was dissolved in an aqueous solution of acetic acid at 40~50 °C, and cooled to about 5 °C. Add sodium nitrite solution with a content of 40% to complete diazotization. Then raise the temperature to 80~90 °C to complete the closed-loop reaction. The oil layer containing methylbenzotriazole is separated from the water layer containing acetic acid, the oil layer is extracted with organic solvent, the extract is distilled under atmospheric pressure to remove the solvent, the crude methylbenzotriazole is recovered under reduced pressure distillation, and then refined by recrystallization method, and vacuum dried at 45~50 °C to obtain purer methylbenzotriazole. There are also after the completion of the closed-loop reaction, without the separation of the oil layer and water layer, directly add sodium hydroxide solution, after coke, diatomaceous earth and sodium dithionite filtration, with 40% ~ 75% nitric acid or 20% ~ 25% hydrochloric acid to adjust the PH value to 5 ~ 5.5, the precipitate is filtered, washed and dried, and a purer methylbenzotriazole can be prepared. There is also a method of using methyl-o-phenylenediamine and ethylhexyl nitrite as raw materials and ethylhexanol as solvent to prepare purer methylbenzotriazole without rectification and refining.