Green building development has stepped into the "deep green" phase, which means that the so-called green building of new building materials and new technologies can neither meet the requirements of the market nor be in line with the national policies. More importantly, although the effectiveness of green building is usually considered at the operation phase, the design phase has always been the most crucial phase for the building to start with a good green foundation. The first key step for a green building is to work out good green building strategy in design and to use suitable building technologies. The article analyzes the important role of digital simulation technology in fine design. With its high reliability, low cost, short project life circle and flexibility, digital simulation technology has become a reliable tool for working out green building planning and predict the future results of all kinds of green technologies.