After graduating from Xiamen University, Chen Jingrun was assigned in 1953 to teach at Beijing No. 4 Middle School. Because he did not speak clearly, he was not allowed to teach classes and was later sent home to recover. In 1954, the president of Xiamen University, Wang Yanan, brought him back as a library assistant, and Chen worked on number theory.
His work drew the attention of the mathematician Hua Luogeng. In 1957, Hua arranged for Chen to move to the Institute of Mathematics of the Chinese Academy of Sciences. In 1966, Chen proved the result now known as Chen’s theorem.