Orientalism emerged as a discipline and produced massive literature on Islam and its different aspects. Orientalists claim that they have introduced and applied Scientific Research method and new research methodology in their research. According to them objectivity, honesty and impartiality are the main features of their methodology.Unfortunately their writings regarding Islam through all ages lack the mentioned features. Study of Orientalist's (of all times ) produced literature about Islam have some common and apparent aspects in their research methodology. In this article those common aspects which may be called major principles while studying Islam and its different fields are being discussed and analyzed which has been deducted after thorough study of literature produced by Orientalism.