During using water from trans-national Lanmei stream, Lanmei cooperation shall be based on governmentally global cooperation in balancing each nation's interests. This paper, aiming at possible water over use issues without united management system, presents Lanmei cooperation based on a case study on Laos Shawn-Thailand Modahan gaming behavior, and theoretically analyzes the water use factors of gaming players. A gaming model is established between two nations which is used to study the strategic selection and evolutional stability. Simulation via Matlab indicates its effects of governmentally strategic selection. Lanmei cooperation should enhance supervision and punishment, increase feedback rate of random inspection to urge governments to use water appropriately. The established differentiated punishment coefficient is of catalysis on gaming shrinking period. Governments will prefer to select rational water use in the global cooperation on Lanmei stream water resource if at a lower developing cost, raised benefits, loss upon irrational water use, and external overflow effect from the other gaming player.