During the rule of King Sejong of the Joseon dynasty, which came after the Goryeo Dynasty, the arithmetic system was reorganized. This period is known as the golden era of Korean mathematics. According to Sejong Sillok (authentic record of King Sejong), Sanhak Gyojeonso (Office of Arithmetic Publishing) and Seupsanguk (Bureau of Learning Arithmetic) were established and many arithmetic textbooks were published. King Sejong himself learned arithmetic from there. The curriculum consisted of five subjects: Sang Myeong San Beop, Yang Hwi San Beop, San Hak Gye Mong, O Jo San Gyeong and Ji San. The first, Sang Myeong San Beop, whose Chinese title is Xiang Ming Suan Fa, explains the elements of metrology, acoustics and computation of series. Yang Hwi San Beop, or Yang Hui Suan Fa in Chinese, contains problems on magic squares and geometric figures. San Hak Gye Mong, whose Chinese title is Suan Xue Qi Meng, deals with solutions of high-order equations. O Jo San Gyeong, with Chinese title Wu Cao Suan Jing, treats accounts, systems of equations and arithmetic series. The Ji San, titled Di Suan in Chinese, pertains to measurements.
The study of arithmetic, which blossomed during the Sejong era, had been deterred to a great extent by the Joseon-Japan war (1592-1598) and the Joseon-Qing war (1636-1637). In particular, a large number of important arithmetic books were lost during the wars. They were restored about a hundred years later during the ruling of King Sukjong (1675-1720). While Joseon was striving to revive the system of arithmetic education, Japan tried to understand the arithmetic books that they took away from Joseon during the Joseon-Japan wars. Japanese arithmetic emerged under the name of Wasan about a hundred years after the war.

The arithmetic bureaucrat Hong Jeong-Ha wrote Gu Il Jip (Collection of Nine One), which consists of three parts of three volumes entitled Heaven, Earth and Human being-nine volumes in total. According to his book, Hong competed with an arithmetician He Guo-Zhu in Qing Dynasty. This is the only record of any international competition in Korean history. From this book we also know that Suan Xue Qi Meng was lost and Tian Yuan Shu was dismisssed in China. (Even the book of counting rods disappeared). He Guo-Zhu was extremely surprised to find that Suan Xue Qi Meng was preserved in Joseon. This finding might have been a stimulus to the Qing Dynasty to reprint the books. Actually Luo Shi-Lin looked all over for the books and at last found three volumes of Suan Xue Qi Meng, printed in Joseon, at Liu Li Chang in Beijing and reprinted them. It is not known how the books came to Beijing, but he was very excited to have found them. He allegedly said that eastern mathematics could not have been transferred without Joseon.

During the later part of the last millenium, Joseon tended to exclude I Ching philosophy from traditional mathematics and also ignore mere practical aspects of mathematics. In other words mathematics became a science independent of philosophy, and Joseon mathematics advanced one step from ideological and from practical calculations.
Nam Byeong-Gil (1820-1869), a mathematician in the gentry class, wrote a book containing old problems selected from existing books. He conducted research on the mathematical properties rather than practical problem-solving methods. His purpose was to establish a systematic or formal framework of mathematics aside from practical mathematics. He also studied with Yi Sang-Hyeok (1810-?), another middle class mathematician, the theory of equations and compared western mathematics with Joseon mathematics. He made conscientious efforts towards modern mathematics. Above all, Yi actively studied werstern mathematics including infinite series through trigonometry.
This shows that he was searching for a way towards modern mathematics. Above all Yi actively studied Western mathematics including infinite series through trigonometry.
Korean mathematics concentrated on the counting rod calculation and Tian Yuan Shu emphasizing the eastern tradition. But the late Joseon era was paving a way towards modern mathematics through independently developed calculations and trigonometry.