Nowadays, with the development of international economy, international investment has become one of the most important ways to prompt global economic development. The number of the bilateral treaties (BITs) and multilateral treaties are increasing as well. These treaties are an important basis for resolving disputes between investors in international arbitration. Many treaties contain a sunset clause. In the field of international law, the use and utility of sunset clauses has remained largely unnoticed despite the fact that they have been employed in major international treaties and agreements.  Nowadays, such clauses have become a core feature in international investment agreements, playing an underappreciated role with the ability to enhance legal certainly in regards to the tension between stability and flexibility. Moreover, sunset clauses complement the protection to investors with the entrenchment effect.  But meanwhile, as one of the important economic entities in the global economic development, the European Union (EU) is trying to terminate all intra-EU BITs, as well as the sunset clauses which contained in the BITs.  This thesis analyse the impact of the sunset clause on intra-EU arbitration after the EU members terminated their intra-EU BITs. Trying to clarify the nature and the utility of the sunset clause in EU law, and try to disengage from the entrenchment effect of the sunset clause at EU and international level.