Abstarct: The human need for presence in open spaces and the influential role of climate in urban activities and behaviors, reveals the need to pay attention to external thermal comfort. In urban open spaces, especially in large cities with warm climates, users of urban spaces are exposed to high thermal loads, which causes thermal discomfort. By controlling radiation and shading, thermal comfort in the open air can be improved. By recognizing the factors that create shadows, such as canopies and their characteristics, a favorable space can be created to enjoy the capabilities of the outdoor space. The new membrane structures have many of the characteristics of nomadic tents such as use of natural materials, daylight, and are very suitable for areas with hot climates by providing shade and natural ventilation. The present study investigates the effect of lightweight membrane canopy on outdoor thermal comfort in Semnan city with hot and dry climate by library and simulation studies with Ansys Fluent, ENVI-met and Lady Bug. According to the studies, the presence of membrane canopy reduces the temperature up to 5 degrees Celsius. The simulation results also showed that the membrane canopy cools the space below and prevents the earth from overheating, Among the four models of: simple membrane canopy, conical, umbrella and saddle, saddle canopy is the suitable model of canopy and has a good performance and creates a cooler space under the canopy. Therefore, saddle lightweight membrane canopy with dimensions of 5x5 square meters and a useful height of 3 meters is introduced as the suitable model of membrane canopy for using by people in open urban spaces in hot and dry climates