The present invention provides a method for preparing acetic acid by carbonylation of methanol, which comprises: passing a raw material containing methanol, carbon monoxide and water through a reaction region loaded with a catalyst containing an acidic molecular sieve with an adsorbed organic amine, and carrying out a reaction under the following conditions to prepare acetic acid. The method in the present invention offers high acetic acid selectivity and good catalyst stability. The catalyst in the present invention does not contain noble metals such as rhodium or iridium, and does not need additional agent containing iodine, and thus does not generate a strong corrosive hydroiodic acid and the like.