Abstract: In 1368 when Ming Dynasty was founded, the political situation of central China was basically formed. Ming Dynasty was getting stronger and stronger and Northern Yuan tended to be weaker. Kory Dynasty during the period of Goryeo U’wang, which had paid great attention to foreign affairs, changed the pro-Ming policies of Gongminwang, resumed the diplomatic relation with Northern Yuan in stead of Ming Dynasty. Such regress of diplomatic relation with Ming Dynasty was, on one hand, due to the influence of Northern Yuan on Kory’s internal politicies; on the other hand, due to Ming’s attitudes toward Kory. In the 14^th year of Goryeo U’wang, Kory witnessed its failure in conquering Liao Kingdom and afterward it resumed the diplomatic relation with Ming Dynasty and stopped such relation with Northern Yuan.