Myths includes an important part of any cultures and shows aspects of Physical and spiritual life of certain people. The culture of the ancient Indo-Iranian peoples was basically formed in a land far from Seas; So, there is no expectation of the existence of traditions or themes related to seas and seafaring in the mythology of this people. However, studying texts such as Avesta, Pahlavi texts, and more in the Shahnameh and other Persian Pahlavi texts, we find signs related to this subject. Undoubtly, this is so important for understanding Iranian culture and civilization. In this research, an attempt has been made to answer this major question that how the sea and seafaring are reflected in Iranian mythology. For this, the mythological role of water, gods related to water, mythological seas and their comparison with real geography, seafaring and shipping in Iranian mythology, epic texts and other related issues is investigated. This thesis has been done by method of historical researches by extracting from sources and researches. The results of this research show that after separating from other Indo-European peoples and entering the Iranian plateau, Iranians became familiar with the seas and seafaring, especially through the Persian Gulf. This phenomenon is reflected in the form of new elements in the narratives and stories of the Iranian epic and myths. Among all these texts, Garshasp-namah has the most such themes.