Postmodernism as a great intellectual movement affected the arts, politics, economics, science, culture, identity, therapeutics and… The present article with help of the documentary and analytical methods intended to analyze the epistemological and sociological dimensions of Postmodernism and introduce its fundamental principles and finally reviewed the various influences of postmodernism on psychology as an interdisciplinary science. Postmodernism is essentially the logic of negation and rejection of the intellectual foundations of any eternal and universal values, emphasize the relative orientation in all affairs. Identity in this regard as the most important aspects of human personality was affected by the change of semantic relativism of postmodernism and other areas of human thought such as women and men in social status, personal identity and social and therapeutic approach.