Although the Parthian dynasty has the longest period of government in the history of Iran, in the Iranian national-epic narrative contained in Islamic sources, the history of this dynasty is very abbreviated. As in most cases, except mentioning the names of the kings and referring to the number of years of their rule, there is nothing else about them. This abbreviation is to the extent that the period of Parthian rule has been reduced to half of the actual time. This case has occupied the thoughts of many researchers and opinions have been expressed about the reason for this abbreviation, the common denominator of all of which is the attribution of this to the deliberate policy of the Sasanians, but regarding the reason for adopting this policy by the Sasanians, so far, a lot of thought has been given to It has not been done. This article tries to investigate the ways and causes of this issue with the historical research method and by questioning the available data. This article shows that, contrary to popular belief, this distortion was not caused by religious beliefs, nor by the hands of the clergy, but by the nobles of the Sassanid court and to solve the political-social problems that the Sassanid court and the Iranian nobles were facing at the same time.