In the present work, optimization of air-cooled heat exchanger using structural theory of Bejan by invoking fluent software has been investigated. Two constraints are applied in the optimization process: the first one is to fix overall area of heat exchanger,A , and second, the ratio of fraction of total heat exchange surface in the fixed pipe, φ. Using these two constraints and the aforementioned theories, the best geometry, that is a symmetric geometry of the tube and the fins was obtained. Furthermore, the effect of parameters such as pressure, Stanton number, ratio of fraction of the convective heat transfer coefficients, ratio of fraction of the conductivity, and the number of fins, etc, was investigated. The results show that for tubular length of 5.8 cm and 4.3 cm radius, the fraction of optimal fins diameter to pipe diameter is 1.88 and the optimal number of fins is 7. By using softwares such as Fluent and Matlab, the fins height, and the distance between the fins was investigated. According to structural constraints, a structure was selected that heat transfer from all the fins are equal. It was observed that the amount of the heat transfer was optimized by 6.2%.