Sun Xin was the younger brother of Sun Li and was married to Gu Dasao, becoming the Xie brothers' (Xie Zhen and Xie Bao) cousin-in-law. Sun Xin was from Liangzhou and a descendant of a family of generals serving the Song Dynasty. He served as a military officer in Dengzhou along with his brother. He was born tall and strong, with eyes which shone with fire and was as powerful as his brother in martial arts, earning himself the nickname 'Little Yuchi' (小尉迟), which was quite similar to his brother's.
