Abstract: Factors such as ammonium salt amount, sulfuric acid dosage and washing procedure on the washing of FCC catalyst were studied. Test results showed that washing FCC catalyst under acidic conditions could consume less ammonium salt to reach the similar sodium oxide content of catalyst. An industrial trial was carried out based on this acidic condition washing procedure and the results showed that about 30% of ammonium sulfate can be saved to obtain the same catalyst quality. Moreover, the amount of ammonia nitrogen in the washing water of FCC catalyst was lowered by about 30%, which is a significant improvement in catalyst manufacture, waste treatment and environmental protection.