A method for preparing high-purity methyl isobutyl ketone (MIBK) from an industrial by-product effluent acetone comprises the following steps: converting epoxide impurities in the effluent acetone into corresponding tertiary alcohol during the process section I; converting acetone into MIBK during the process section II; and realizing conversion of the above tertiary alcohol and separation from MIBK through reactive distillation. In cooperation of optimal refining process, a high-purity MIBK product can be easily prepared. By the technology, the byproduct effluent acetone is converted into an MIBK product with high added value. The equipment has remarkable economical benefit.