Offgas problem of wastewater treatment systems is becoming an increasing problem, as the public's living standard and awareness of environmental issues increases. This article puts forward the necessity of cleaning the offgas from wastewater treatment facility, introduces the harms of odorous portion of offgas to public and concrete construction, brings forward the main object of offgas emitted from wastewater treatment plant. The way of restraining the generation and escaping of gases, the containment structure of facilities and decontaminate of offgas after it emit, and the virtues and shortcomings of each method are discussed in this article to give advices for the selection of controlling ways.