Petrochemical wastewater was pretreated by hydrolysis acidification to improve the biodegradation and treatability on limited aeration conditions. The results showed limited aeration with DO from 0.2 to 0.3 mg/L (average ORP was -210 mV) was the best condition. The BOD5/COD of influent was 0.23, and it increased to 0.43 on this condition. Limited aeration can obviously reduce the reduction of SO42-, reducing the generation of toxic gas H2S, and almost no H2S can be detected in the off-gas. The sulfate reducing bacteria (SRB) diversity and abundance on limited aeration condition was obviously inhibited. Limited aeration condition was benefit for the removal of benzene ring organics, such as benzene, toluene, ethylbenzene and xylenes (BTEX), improving the toxicity and treatability of the wastewater. Based on the experiment results, an anaerobic hydrolysis acidification tank (100,000 m(3)) has been transformed into limited aeration hydrolysis acidification tank and it runs well. (C) 2015 Published by Elsevier Ltd.