In the modernization of the history, most Asian countries believe the invention of oriental tradition has been biased by the imperial ideology. They have set up a political system for the rewriting of the national history by starting with a new view concerning the ancient history. During the process of imperial modernization, Thailand has the imperial biased product concerning the canonized ancient history in which Thai scholars have attempted to rewrite Thai ancient history and reestablish it as the official history over 100 years ago. However, it has neither been adopted as the authoritative history of Thailand nor been circulated in the school textbooks in Thailand. This study attempts to find existence of official Thai history which is based on the fact and reality. This dissertation focuses and tracks down the establish process of Damrong history, in which the modernization used to mislead in order to provoke fundamental problems for no-adoption of the canonized history for the forge both Ramkhamhaeng King epitaph and foundation of the Ayutthaya Kingdom. Also this dissertation proclaims the reason of nocirculating the school textbook regards Thai ancient history as well. This dissertation proves the prolonged Lawo Kingdom for more than 400 years, because Ayutthaya Kingdom has not founded since 1351 but since 1082, which had 9 kings more before PhraRamathibodi First. This dissertation had a different historical period summary regardless of the traditionally inventional history : Iron Age(600 B.C.-A.D. 250), Dvaravati Age(A.D. 600-1100), Lawa Age (A.D. 1100-11C), Ayutthaya Age(11C-18C), Thonburi Age(18C), Ratanakosin Age(since 18C to the present). This dissertation still has the question of start-up of Ayutthay Age and the fact or forge of Ramkhamhaeng King epitaph as a limitation of Thai ancient history.