Common European identity can be defined as a set of secular-based cultures and values shared by all the citizens of the European Union. Theoretically, there is a European identity alongside other national or cultural identities, and in fact, people have the identity of hierarchical and multi-layered identity in terms of national or cultural significance. Strengthening a common European identity in which the Europe Union's people consider secularism-based culture as the base of their political, social, cultural and economic values and norms, is vital for the long-term integrity of EU. EU member states, despite religious and cultural similarities and commonalities, have subcultures which have led to their own identity. As a result, they have a different strategic culture and strategic priorities. This different strategic culture is among the key factors that made these countries, especially in times of crisis, not reach a coherent security and defence policy. For analysing the various aspects of culture in Europe and the place and its impact on a common European identity, on basis of the theory of constructivism and strategic culture approach, we can say the secularism-based culture can be considered as a core layer of common European identity and has played a fundamental role in EU integration and also considered the main criteria for the admission of new members to EU.