Green building is inevitable tendency in development. However, most of the developers in China are still waiting for the best timing. Compared with the ordinary ones, green buildings have features of more investment, higher risks, and more repayments. It is suitable for commercial property with consideration of life-cycle cost. How to choose the best timing of investment for commercial green buildings is important and urgent. This paper establishes a decision-making model with the real option theory for green buildings investment opportunity in commercial property and provides some advices to developers creatively, and tests the model by using a numerical simulation with an actual development project's data. It gives method for developer decision-making and advices to government for green building promotion.