The invention relates to a method for cleaning a three-way catalytic reactor of an automobile. The method includes the following steps: (1) demounting an oxygen sensor near the three-way catalytic reactor, and exposing an installation hole of the oxygen sensor; (2) inserting a cleaning pipe into the front end of the three-way catalytic reactor via the installation hole of the oxygen sensor, and performing cleaning agent cleaning on the three-way catalytic reactor through a cleaning agent emitted by the tail end of the cleaning pipe; and (3) pulling out the cleaning pipe after cleaning agent cleaning, inserting a steam reduction pipe into the front end of the three-way catalytic reactor via the installation hole of the oxygen sensor, and performing steam reduction on the three-way catalytic reactor through steam emitted by the tail end of the steam reduction pipe. The cleaning method can clean the three-way catalytic reactor without demounting the three-way catalytic reactor, can effectively shorten the working time, and can improve the cleaning efficiency; and through combination of cleaning agent cleaning and high temperature steam reduction the three-way catalytic reactor can effectively restore to a good working state, and the cleaning effect is improved.