Building Energy Efficiency is one of the most important goals for green architectural design. Natural ventilation is a building energy efficiency technique adapting to the environment. Compared with air conditioning, natural ventilation can reduce the energy consumption and bring new air to indoor space. However, air environment, as an important aspect of building optimal design, can be ignored easily in traditional research, the quantitative analysis aiming at the energy efficiency of natural ventilation is less. In this paper, we use Fluent Air-pak software and Wenyuan Building of TongJi University as an example, to analyze the air flow field of indoor natural ventilation and provide the method and theory of air-environment design.