Courtyard has been recognized as one of main elements in the Iranian culture, architecture and building design. According to its micro-climate effect in improving thermal performance of building, courtyard has been considered as a considerable subject for many researches. This paper investigates the courtyard’s design parameters and geometric configurations in pre-design states for improving thermal performance and comfort. For achieving this point, in this research the influence of courtyard orientation, horizontal dimensions and other parameters related to geometry have been evaluated. Due to micro-climate effect of courtyard on parameters related to thermal comfort, three main geometric layouts such as closed, semi-closed and open geometry have been investigated and compared by CFD simulations in ENVI-met software. The thermal comfort parameters are also investigated through comparing mean PMV in all simulations cases, using Fanger’s extended model. The results showed that thermal performance of closed shaped courtyard is better than other layouts. Also the comparison of results related to different aspect ratios (length to width ratios), put into evidence that thermal performance improves as the aspect ratio gets close to 1. That means as the courtyard shape encloses to square, the thermal performance improves and the mean air temperature in the investigated microclimates declines. To determine best configuration for Tehran’s climate, the results showed north-south orientation of building and increase of the height of the courtyard, are the two most appropriate considerations that will directly improve the thermal performance and comfort, specifically in closed and semi-closed layout.