In order to protect the wetland resources, the government designated many wetlands nature reserves, forbidding farmers to exploit and utilize them. This treatise proposes an effective means of resolving the externalized problem of establishment of wetlands nature reserves——ecocompensation from the angle of externality theory. Take Tianjin Qilihai wetland as an example, the paper analyzes the externalities to local peasants associating with the establishment of wetlands nature reserves at first. The negative effects included: limiting their survival rights, development rights and environmental rights, more importantly the psychological impact on the local residents. That was to say the establishment of wetlands nature reserves did harm to the vital interests and rights of local farmers to some extent. And then the paper clearly expounds that the city country government, surrounding areas, and local enterprises and institutions that benefits from the reserves should become the local subject of ecocompensation. Finally, the value of the wetland is monetized and then the compensation standard is fixed based on the value.