Abstract: A 3-D numerical simulation of natural ventilation process in a tunnel type greenhouse was performed with the help of software CFX to investigate the influence of wind direction outside on the airflow pattern inside and how the openings, door and side openings acted when the natural ventilation process was stable. The simulation was carried out under two typical wind directions: parallel and 15° to the greenhouse ridge, respectively. Result shows that on the condition of wind direction outside parallel to the greenhouse ridge, airflow enters into the greenhouse through frontispiece-open and the first half of the side windows, and departs from the remaining part of the side-windows. The overall airflow rates reach comparatively higher at tunnel central area and lower at the vicinity of sidewalls, the end part and top of the tunnel reveal many complex airflow patterns; Under the condition of wind direction 15° to tunnel ridge, air flows in mostly from the indward side opening and the frontispiece-open, departs from the leeward of side opening, there is an overall deflexion of the main current stream inside and various vortices are formed to produce the collision of airflow between sidewalls and air current, which makes airflow much more complex. The direction of wind outside has a major effect on the airflow pattern inside the tunnel greenhouse.