Abstract: Environmental civil nonprofit litigation is a legalized way for environmental protection organizations （EPOs） to express， deliver， and actualize their interest appeal. It can activate the endogenous force of social governance，cultivate social capitals，and form a social counterbalance ofauthority. Yet，EPOs in practice do not exhibit sufficient intentions of litigation，which has gravely weakened the effect of this system. The legal opportunity space of EPOs participating in nonprofit litigation has been severely squeezed by expensive litigation cost，the court’simpertinent activation of case filtering mechanism，the strong contention of procuratorial work in environmental nonprofit litigation，and the functional overlapping of different systems. The combination of the above factors makes EPOs reluctant to participate in nonprofit litigation. The theory of legal opportunity structure is a new and systemic perspective for the study on the impetus and aspiration of EPOs’participation in environmental nonprofit litigation. On the five dimensions of increasing effective legal supply in relation to environmental nonprofit litigation，perfecting the litigation cost sharing system，advocating multi-party collaborative participation， promoting the renewal of environmental judicial ideas，and strengthening legal conviction，the theoryexpands the legal opportunity space of EPOs to institute an environmental civil nonprofit litigation. It makes environmental judicial remedy more open and accessible and enhances the aspiration of EPOs to express，in a legalized way，their interest demand and safeguard environmental public interest 。

Key words: environmental nonprofit litigation；environmental protection organization；legal opportunity structure