The investigations of special safeguard measures to China initiated by the U.S. International Trade Commission are based on Section 421 of the Trade Act of 1974. As the Section 421 is too simple，International Trade Commission has to make legal interpretation and establish agency practice to make determinations. In U.S.， although agency practice is not a source of law， requested by “Due Process” in administrative procedures， agency practice still has a kind of binding force to agency decisions. Since agency practice is highly respected and believed by agency but in the meantime not a source of law，Chinese enterprises should classify from dif erent types of agency practice and prepare for the corresponding strategies.