分裂政權之間相互遣使往來之事古已有之，不僅是政治、軍事上的外交談判，也是合縱、連橫的手段，更是收集對方情報的有利管道。南北朝自北魏奠定以散騎常侍擔任外交使節的常規以來，基本上南朝與東魏、北齊都遵循此一慣例。然北周採周官之制，其對外交使節的選派方式也略有不同。從實際案例中檢視，北周並無以某一官職擔任外交使節的常規或慣例，而較多以專人專才負責某方的外派事務，如楊荐經常出使柔然、突厥，杜杲則一再出使陳朝。不過在此一大原則之外，尚有一些小原則與官職有關。案例中可見御正、御伯與納言多次擔任外交使節，其原因可能與御正屬中書系統、御伯與納言屬門下系統，皆與散騎常侍同為掌王言性質之官職相關。

It is a tradition that regimes sent envoys mutually during the period of disunion. It’s not just for diplomacy negotiations, but the way to collect political and military information about the other side. Since Northern Wei established the rule of appointing Sanjichangshi（散騎常侍） to be an envoy, both Southern Dynasty and Eastern Wei/Northern Qi continued practicing this rule. However, Northern Zhou was under Zhouguan（周官） structure, and the way to appoint envoys was very different. Examining the practical cases, Northern Zhou often nominated envoys according to their ability more than their political position. Yang Jian（楊荐） for Rouran, and Du Gao（杜杲） for Chen Dynasty were examples. On the other hand, Yuzheng（御正）, Yubo（御伯）, and Nayan（納言） were also sent on diplomatic missions frequently. Probably because Yuzheng was belonging to Zhongshu（中書） system and Yubo/Nayan was belonging to Menxia（門下） system, both of these two systems were in charge of the expression of emperor’s opinions.