The 25-year strategic cooperation agreement between Iran and China that was signed on 27 March 2021 first announced in 2016 during Xi Jinping visit to Tehran, at a time when sanctions on Iran were being lifted as part of the 2015 nuclear deal. Chinese and Iranian officials have been working out the details of the deal ever since as part of a slow process of consultation and negotiations. This process was doubtless complicated by the sudden uncertainty created by Washington’s abandonment of the 2015 nuclear deal and decision to re-impose sanctions on Iran from 2018 onwards. However, negotiations between Iran and China accelerated again as U.S.-China tensions increased and Beijing began looking for ways to push back on what it calls American "bullying," such as the extraterritorial sanctions imposed on Iran. With regard to above- mentioned statements, the main question of research is that how does the US play a critical role in forming the Iran-China strategic agreement and its future success? The hypothesis is that one of the influential factors in shaping of the 25-year strategic agreement was the US policies towards Iran and China. In other words, Washington hostile behaviors and measurements towards Tehran and Beijing has paved the way for the latter's further rapprochement and cooperation. Despite of the fact, meanwhile, the US could enact as a destructive factor since the agreement is not based on its national interests. The research method is analytical- explanatory and neo-realism theory is applied as theoretical approach.