The legality of unilateral sanctions has long been controversial. From the perspective of sanctions resolutions of the Security Council, some enforcement sanctions exceed the authorization of the Security Council, the legality of which cannot be obtained from the resolutions. From the perspective of primary rules such as special international law (treaties) and general international law (custom), many unilateral sanctions may violate treaties and customary law of legislative jurisdiction and the principle of non-intervention. However, the exception clauses of treaties and customary law leave legal space for some sanctions. From the perspective of the secondary rule of state responsibility law, the rule of countermeasures has provided a defense basis for unilateral sanctions to preclude wrongfulness. Therefore, it is difficult to identify unilateral sanctions as legality or illegality. We should make analysis and judgment combined with specific sanctions and relevant rules of international law. China can deal with extraterritorial unilateral sanctions from the legal perspective and seriously consider the legality of foreign sanctions in legislation and practice.