Afforestation on a large scale has a possibility to be a countermeasure against the global carbon dioxide problem. There are, however, many problems that should be solved. In the present paper, the importance of systems approach of greening is emphasized and discussed. The systems adopted here are the system of land utilization, social and industrial, and energy supply as well as the estimation method of energy balance. And also several technological problems are discussed in terms of construction of ecological model and simulation of artificial rainfall for water.