The control of outdoor thermal comfort became a question of extreme importance in hot desert cities, knowing that people of these cities seek to shelter solar rays by all means especially during the hot season. The aim of this research is to study and analyze the effect of urban vegetation and shade on the microclimate and thermal comfort within an open public space in a hot desert city (the city of Ouargla in Algeria). As an element that minimizes and intercepts the sun’s rays, it generates solar energy shade and absorbs the fluxes of radiation, modifies the temperature, the relative humidity and minimizes the wind velocity and modifies its directions. For this, we have used Ray Man which is simulation software to calculate the indices of thermal comfort. The work consists in calculating these indices before and after the insertion of two types of vegetation within our case study (the martyr’s plaza in the traditional neighborhood of the city of Ouargla). The results obtained show the main role of vegetation by the improvement of thermal comfort.