Green software has become an important research objective. And virtualization technique is the main implement method now. In this paper, we introduce four concepts describing virtualization as virtualization process, virtualization process capability, virtualization efficiency and virtualization process maturity to measure the mature extent of implementing virtualization, and further present the related reference model for green software to evaluate the software virtualization degree. Here four levels in this model are defined. Each level describes the degree of green characteristics for software. And the model framework and the model structure are presented. Thus the technique and management methods of every level are described in detail.