The purpose of building greenhouse is to provide ideal conditions for plant growth and environmental factors control in order to provide optimum conditions for the plants. In many regions of Iran the same structure model is used for greenhouse structures. However, the variation of climate and the type of cultivated plants, optimal greenhouse structure study of regions is necessary. It is obvious, the optimal structural influence on energy costs decrease heating and cooling energy. Regional climate and the type of crop are the most important factors influencing greenhouse structure and its performance characteristics. Due to the variety of climates in Isfahan region studies on issues related to greenhouse structures and structural modeling to comply with the conditions of climate were considered. After gathering weather data for the regions, greenhouse structure modeling was done to comply with climate conditions. Four common greenhouse structures by SAP2000 software were modeled and designed. Load including dead load, live load, snow load and wind load were forced for both climates and structural force analysis was performed. Optimal and consistecy for climate conditions of the structure, tunnel structure with vents wings of a dove and optimal structures with climatic conditions of Meimeh, the arched tunnel structure was selected. For numerical simulation of airflow and heat transfer (greenhouse natural ventilation), greenhouses to different configuration roof and side vents and perpendicular and parallel wind direction to the length of the greenhouse was considered. Turbulent flow of air inside the greenhouse in three dimensions, using FLUENT software k epsilon (k-?) model was simulated. The simulation was performed using FLUENT software to solve Navier-Stokes equations.The cucumber shrub were simulated using the porous medium approach.Contours of the air velocities, temperature distribution pattern and flow pattern inside the greenhouse on optimal structures were determined. According to the results of simulation for both types of greenhouses, in the case where only the roof vents is open, the temperature distribution pattern and contours of the air velocities respectively, almost 10 ?C temperature differences between the inside and outside of greenhouses and the lowest indoor air flow velocity is showing. In the case of where only side vents open, the temperature difference inside and outside the greenhouse and plant canopy was about 4 to 5 ?C and warm air 10 ?C higher than the external temperature in high and near roof vents has accumulated. While the side vents and the roof both were opened greenhouse inside and outside temperature difference was about 3? C. The results showed when only roof vents are open, the lowest ventilation and cooling is done by natural ventilation. Also, if the greenhouse side and roof vents are open air mixing and temperature distribution inside the greenhouse and plant canopy is more uniform. Keywords: Greenhouse, Structure, Ventilation, Simulation.