In 1944, he was appointed president of the Shiguang Catholic Church. On June 9, 1949, Pope Pius XII appointed Duan as bishop of the Roman Catholic Diocese of Wanxian. He was ordained bishop on October 18 of that same year.[1]
After the establishment of the Communist State, he successively served as director of the Sichuan Catholic Partnership, member of the China Catholic Partnership, vice-chairman of Sichuan Catholic Partnership.[1]
In 1998, Pope John Paul II invited Duan to attend the special session of bishops in Asia. He could not travel without a passport.[1]