The effects of vent configuration and wind regime on the microclimate in the tunnel greenhouse were numerically investigated. A full scale computational fluid dynamics model (CFD model) was constructed based on a tunnel greenhouse cultivated with water spinach in eastern China. The model was firstly validated by comparing CFD simulations with experimental temperatures. The simulations had similar trends to those of the experiments with less than 1.1℃ of difference. It was then employed to investigate the greenhouse airflow and temperature patterns with different vent configurations, evaluate the effect of vent configuration on the ventilation rate, temperature difference between inside and outside, and the inside climate homogeneity, and reveal the greenhouse microclimate mechanism with different wind regimes. Simulations showed that different vent configurations induced different inside microclimate patterns and ventilation performances. The roof plus side opening provided the highest ventilation rate, the minimum temperature difference and a relatively uniform indoor climate, and thus can be recommended for summer ventilation. Wind regime had a significant impact on the airflow and temperature patterns in the greenhouse, which considerably affected the cooling performance and the indoor climate homogeneity. With the weather conditions of high temperature and low wind speed, thermal driven ventilation played a remarkable effect on the greenhouse microclimate. The roof and side opening can improve greenhouse cooling performance remarkably and reduce air temperature in crop canopy effectively.