This study examined the form of diplomatic documents exchanged between Goryeo and Khitan during the war in 994 and compared it with the documents exchanged between Khitan and the Five Dynasties and Ten Kingdoms in 10th century. Since its founding in the early 10th century, Khitan had established diplomatic relations with the Chinese dynasties. In the early days, they served Later Liang as a servant and maintained an equal relationship with the Later Tang. The Emperors of the Later Jin and the Later Han once recognized the Emperor of Khitan as their monarch. Since the 950s, the emperor of Khitan had taken the form of a parallel relationship with the Emperor of the Later Zhou and Song, while neighboring North Han and Western Xia treated him as their monarch. Throughout the 10th century, Goryeo had maintained a friendly relations but had little contact with the Five Dynasties and the Song. By the end of the 10th century, Goryeo and Khitan recognized each other as a direct military threat, and the crisis immediately led to war. However, the two nations, which did not want to a full-scale warfare, sealed the conflict by establishing diplomatic ties. At this moment, Goryeo King sent an appeals (表文) to the Khitan Emperor, who replied by a form of edicts(詔書). This protocol was to confirm that there was a Suzerain-Vassal relations between the two at a ceremonial level. However, since then Goryeo had consistently made diplomatic contact with Song. This implies that the Suzerain-Vassal relationship between Khitan and Goryeo was not exclusive to Goryeo’s other diplomatic relations. In this process, there is little evidence that Goryeo had taken a negative attitude toward the establishment of relations with Khitan saying that they are barbarians. These diplomatic practices had been maintained for a century, and both countries had established a stable relationship without major conflicts.