Foreign cases and experiences of horizontal cooperation mechanism for cross border water environment management will be introduced in this paper, including the joint implementation of the Convention on Water Quality in Great Lakes by the United States Government and the Government of Canada, the EU Water Framework Directive by EU member governments and the cross-border administrative cooperation within the basin, the cross-border watershed pollution control by the nine countries in Rhine Basin, and the inter-regional coordination and cooperation in the Thames River Basin. Besides, by taking reference of the horizontal coordination and cooperation between the relevant national departments for biological diversity in Norway, analysis and summary were made about these cases in terms of the coordination mechanisms, policies and legal coordination, overall planning, operation process, the scientific and technical support, and so on. The foreign successful experiences in trans-boundary water environment management include: (1) a strong coordinating institution which is able to exert influence on the economic decisions by governments involved with trans-boundary water bodies; (2) strict enforcement of the laws and regulations developed by all the governments involved; (3)coordinated planning which takes the trans-boundary water body as an ecosystem, unify management, and clear responsibilities and obligations for all related parties; (4)the need for an effective technology institution to provide scientific support for rational and sustainable trans-boundary water environment management; (5)continuous innovation and improvement of management technologies. These experiences have important implications for the domestic cross-border water environment management. For the trans-boundary water environment management, the establishment of and innovation in the trans-boundary water management must be compatible with existing economic and social structures and mechanisms; the management of trans-boundary water is a process of constant modification, improvement and complementation; strict enforcement of laws is the guarantee of effective management; academic counseling and support is extremely important for the management; the fully integrated river basin management is the only route leading to success; the international and inter-sectoral cooperation under the same overall framework is an effective way for the trans boundary water management; the transboundary water management is a long-term, arduous task.