This study establishes a scientific, reasonable, and feasible comprehensive evaluation system for green building's power supply system design and implementation to achieve optimization of their thermal, environmental, and economic performance. Unlike traditional evaluation methods that use single index such as economic performance or exergy efficiency for the criterion, the proposed evaluation method takes annual revenue, exergy efficiency, CO2 emission, and system reliability as indices. This advanced comprehensive evaluation method is based on a combination of the method of the gray relational analysis (GRA) and the analytic hierarchy process (AHP) to assess the multiobjective performance of building's power supply systems. The method is applied to compare four kinds of the power supply system of a hospital to determine the optimal system. The result shows that the system which combines cooling, heating, and power supply systems (CCHP) adding solar photovoltaic (PV) panels has the best comprehensive performance when the capacitance of solar PV panels is large enough.