Abstract: Article 30.10 of United States-Mexico-Canada Agreement(USMCA) imposes the unilateral obligation on its contracting parties not to sign a free trade agreement with a non-market country. In nature， this clause is an expulsion clause， not a withdrawl one with the aim at forcing the contracting parties to cut off the trade relations with China as none of the United States， Mexico and Canada has recognized China as a market country. The US government official did not hesitate to claim that this clause is a poison pill clause which will be copied to other FTAs. Confronted with these new restrictive measures imposed by the western countries led by the United States on China， we need to face squarely the logic behind the concept of the non-market country and the difficulty of the remedies for it. As the United States is trying to disable the WTO， the legal analysis on the illegality of the poison pill clause will help us to understand better the nature of trade protectionism and the significance to safeguard the multilateral trading system. Meanwhile， China may also dissolve the negative effect of those restrictive measures by its active engagement in those regional trade agreements.

Key words: United States-Mexico-Canada Agreement(USMCA); non-market country; poison pill clause; illegality