The Jame' Mosque of Ardestan is one of the famous buildings of the fifth century in Iran, which is known in the field of architectural studies of the Seljuk period, as a clear example of the architectural features of this period. However, this mosque has been neglected and no detailed studies have been conducted on it. What distinguishes this building as the subject of this research is the geometric shape of the transition area (ChapireSazi). This geometry presents a different structure compared to buildings of the same period. For this purpose, preliminary information was collected through direct field observations, interviews with masters of building restoration and library studies. Then, using a descriptive-analytical method, the construction of the dome structure of the Jame' Mosque of Ardestan has been investigated. The results show that in the ChapireSazi of this dome, a new method has been used to build a corner called "Patkaneh". This method is based on fractal geometry, which has similar and self-organized structures.