The large iwan of Taq Bostan and its reliefs with a number of other reliefs of Sassanid era have always noticed due to the used beauty and art in its structure. However, there have been disagreements in recent centuries regarding to its antiquity and it is not clear that it belongs to which Sassanid kings due to the lack of an inscription on its iwan. In this regard, although most archaeologists have attributed the first generation of the large iwan of Taq Bostan and its reliefs to Khosrau II, some comments have recently proposed attribution of the relief of Taq Bostan to Sassanid Peroz and Ardashir III which have questioned its antiquity and assignment. Therefore, the present study describes the Taq Bostan reliefs and considers the proposed point of views in order to analyze the large iwan of Taq Bostan due to the significance of it and determining its antiquity and attributing it to Sassanid Shahriyar. Accordingly, most probably the relief of Taq Bostan belongs to Khosrau II with comparative study of historical and archaeological works including the crown, crown reliefs, face components, clothes, capitals of Kermanshah, coins and using historical references which will be presented.