The invention belongs to the field of fine chemical technology, and relates to a method for preparing 2,2,4-trimethyl-1,2-dihydroquinoline. Yeast is used as a biocatalyst, in a specific biotransformation system, isobutyraldehyde or 4-methyl-2,3-pentanedione is added, culturing is carried out at 0-50 DEG C for 10-1,000 minutes, and centrifuging is carried out for removing thallus to obtain a fermentation broth; and a solvent is added into the fermentation broth for extraction, then aniline is added, heating is carried out to the reaction temperature, and after reaction is carried out for a certain period of time, distilling is carried out for removing the solvent to obtain 2,2,4-trimethyl-1,2-dihydroquinoline. Strong acid is not used as a catalyst, liquid-alkali neutralization and water separation processes are not needed, that is, no waste water is generated, a biological transformation method is used, yeast can be reused, meanwhile, the problem that raw material acetone is volatile during the reaction process is solved, the reaction temperature is reduced, the reaction time is shortened, and an environmental-friendly synthetic process is formed.