Architects and artists have long been fascinated by the use of geometric decorations in the construction of buildings, especially religious buildings. In this paper, some geometrical In this article, we have tried to compare some of the landmark designs of the two buildings of Kerman Jame Mosque (755 AH) and Yazd Jame Mosque (724 AH). Kerman Grand Mosque is one of the 700 year old four porch mosques that have a lofty entrance, courtyard, porch and nave. Its construction began in (705 AH) by the order of Amir Mobaraz al Din Mohammad Mozaffari Meybodi, the head of the Mozaffari dynasty, which ended at the end of (755 AH). Inspired by Sassanid architecture. Its eastern entrance was destroyed by the firing of Agha Mohammad Khan and was later repaired. Yazd Grand Mosque has been built in the style of a porch in the heart of the desert during a century (6th century AH) in different historical periods, the most important of which are Ilkhanid, Safavid, Timurid, Al Muzaffar and Qajar. Over time, it was built by several founders, but the main foundations of the mosque were built by the Sassanids. The current building of this mosque is considered to be Azeri architecture in two seasons. The purpose of this study is to expand the field of recognizing and introducing the cultural resources of our country through analysis and introduction of geometric patterns of these two buildings according to the subtleties hidden in the geometric patterns used in these mosques and discovering the mystery hidden in them. The questions we are trying to answer is 1 how to compare the geometric patterns of these two mosques by comparing the geometric patterns used in the comprehensive mosques of Kerman and Yazd? 2 Considering the restoration, reconstruction and annexation of parts to the buildings of both Yazd and Kerman mosques, what are the most important stylistic features preserved in the geometric designs of both mosques during different historical periods? Using descriptive analytical method and conducting library research in the field of architectural arrays of these two buildings And field research has evaluated and comparatively compared the geometric patterns of these two buildings of the Iranian architectural index. The method of data collection is documentary and based on visual field research (photography) and according to the value of observations, perceptual mapping method has been used to explain the visual stages. The research findings show that considering the precedence of construction of Yazd Grand Mosque over Kerman, the possibility of modeling and adapting this mosque by the artists of Kerman Grand Mosque seems probable. The construction of both the Yazd and Kerman mosques did not only include a historical period, but also different periods. Each of these two parts has been built over time by several founders. The governments: Ilkhani, Teymourians, Al Muzaffar, Safavids and Qajaris have played a role in completing parts of these two buildings, but the whole of Kerman also has Zandieh motifs. The main features of the designs in the Yazd Grand Mosque are mostly based on patriarchal and Timurid features. . The predominant style of geometric designs in the Kerman Grand Mosque is Ilkhani and Mozaffari. The geometric designs of Yazd and Kerman Grand Mosques have differences and similarities, among which there are many more similarities than the differences that can be considered as the common spirit of their geometric designs. Since both mosques were built in different periods, one cannot expect a geometric pattern from a historical period in both mosques. But it is interesting that the main spirit and extract of the geometric designs of both patriarchal mosques and in later periods with the knowledge that has reached them from previous masters, this Ilkhani extract has been preserved. Subsequent masters have tried to present harmony and unity with the previous designs and have practically followed in their footsteps. And the observer of these geometric patterns practically does not notice the inconsistency in the patterns which is the result of obvious differences in design. If we want to evaluate the geometric designs of these two buildings in terms of style, Yazd Grand Mosque is more inspired by patriarchal and Timurid architecture, which is close to the Azeri style, and in terms of geometric designs is more «logical and complex» than Kerman Mosque. On the other hand, the geometric designs of the Kerman Grand Mosque are mostly inspired by patriarchal and Mozaffari architecture. And in terms of form indicators, geometric patterns in the field of «expression of emotional states» in form and color is a valuable example.