The integer scale method (Zhengshu Chifa in Chinese and Kansu Hashiraken Sei in Japanese) is a traditional architecture design method of traditional timber structure in the early period of East Asia. According to Shiqing Zhang, this method have been used in the existing biggiest timber structure remain of Chinese Tang Dynasty the main hall of the Fogongsi Temple and according to his research the restored length of the carpentry ruler of this building is about 29.6 cm long. This study analyzes the real measurements in the report of 2008 on this building from the perspective of the integer scale method and realizes that this building should have been designed and constructed with the carpentry ruler of the length of 31.46 cm, while there should have been another modulus of one third foot (a length unit in Tang Dynasty, also named Tangchi in Chinese) long. Further just because the height of Cai in this building is just about one Tangchi long the design scheme speculated by the authors be the result of both the Integer Scale Method and Caifen System. This study has penetrated into the details of technology of this building and is meaningful in both the understanding on the integer scale method and the research on the history of the scale in Chinese Tang Dynasty.