Abstract: The frequent occurrence of environmental mass incidents has become a key factor affecting social stability. And its Internet public opinion develops rapidly with profound influence. Therefore, it is of great significance to discuss the guidance of Internet public opinion on environmental mass incidents. Through multiple case analysis of 24 typical environmental mass incidents from 2005 to 2017, it is found that Internet public opinion guidance of environmental mass incidents includes seven elements: multiple participants, unobstructed channels of interest expression, active Internet agenda setting, online and offline linkages, timely information disclosure and response, complete Internet public opinion monitoring and early warning, and stable institutional support. The types of environmental mass incidents play a role in the relationship between the guiding elements of Internet public opinion and the results of environmental mass incidents.