Inter-Organizational Cooperation is the most common and important strategy in modern public and privet sectors managerial activities. In this paper the concepts of inter-organizational cooperation means not selfish cooperation as in the game circumstance and theory, but general collaborative action between organizations, they have share same goal. The achievement level of jointed-goal of inter-organization is depended upon the performance of cooperation, which resulted from the conditions and circumstances of cooperation. This paper analyses the effect of inter-organizational cooperation on achievement level of the jointed goal between two organizations with computer simulation model of the system dynamics approach. In the computer simulation model, three factors, goal perception, communication, and control, are considered as a key conditions of cooperation, which impact on the performance of cooperation. Simulation model was constructed with focus on the dynamic interactions between these three factors and the achievement level of jointed-goal. Consequently, the results found in this paper may provide further grounds for reducing the time delay that included in the conditions of cooperation.