Abstract: Aiming at the effectiveness of EPC project organization interface management, we present an effectiveness evaluating index system of EPC project organization interface management from four aspects as information, personnel, work processes and materials. The collected index data were verified by SPSS and AMOS software to ensure the reliability of evaluating index system. Through reformed gray-clustering method, we determined the grey clustering weight，the comprehensive clustering coefficient of each index and its class and the evaluation results. In the example of organization interface management of Youchou Hydropower Station, the evaluation result belongs to middle grade level and the deficiency of information management is the main cause for the low efficiency of the organization interface management, which verifies the feasibility and effectiveness of the proposed method.