This paper examines how Joseon’s understanding of the Shixian li method improved in the early eighteenth century. To this end, this paper focuses on the year Euryu calendar affair, particularly the ways in which Gwansanggam astronomers dealt with it. The argument of this paper is that Joseon astronomers were able to make improvements because there had already been prior work in the late seventeenth century, conducted by Gwansanggam astronomers who desired to learn the Shixian li method and by a few yangban 兩班 officials such as Nam Guman 南九萬 (1629-1711) and Choe Seokjeong 崔錫鼎 (1646-1715) who believed in the accuracy of Western astronomy. These scholars organized a study group for learning the Shixian li. This paper also shows that the Gwansanggam and the yangban officials ingeniously utilized the year Euryu calendar affair as an opportunity to persuade the king and his court to support their astronomy project.