Abstract: Su Xun and Ouyang Xiu's friendship began with letters. It was once believed that Su Xun did so for his sons' examination and development in the capital, but it is not the case. Investigation of related documents shows that their academic exchanging not only reinforced their strong friendship, but also had far-reaching and constructive effect on the development of Ancient Prose Movement in the Northern Song Dynasty, though they had different views on literature and Tao, human and Tao.