Micro-grid is one of the main ways to connect renewable energy to power grid, and it is an important research content of smart grid. Objective and effective evaluation of the performance of the micro-grid has important guiding significance for improving the energy optimization of micro-grid operation. Based on the optimal membership degree of fuzzy evaluation method, this paper make a detailed analysis for micro-grid from reliability, quality, economy and environmental protection, and then it proposes a new comprehensive evaluation method suitable for the operating performance of standalone micro-grid .The proposed method can effectively evaluate the comprehensive performance of micro grid operation over a period of time. Finally, this paper analyzes the actual operation data of an island, proves the validity and rationality of the method.