Through analyzing generation and control of environmental opportunistic behaviors, we considered that environmental audit originated in something which aimed to restrain environmental opportunistic behaviors. We concluded when the environmental opportunistic behaviors were very serious and beyond the toleration of society, people would have supervisory review requirements and accountability requirements, and then environmental audit would appear. Finally, we analyzed environmental investment, environmental governance and energy consume data, then we concluded that the audit to budget execution used in environmental departments was caused by the accountability of environmental investment, and accountability about pollution of water and its governance. It is to verify the concept that environmental audit comes from and changes with the demand of environmental accountability.