Huai Su was one of the two great Kuangcao calligraphers of the Tang Dynasty, a native of Tanzhou (present-day Changsha, Hunan Province). He became a monk in his childhood. He was more than 20 years younger than Zhang Xu(the other Kuangcao calligrapher) and learned from Zhang Xu's and Yan Zhenqing's work. His style was mannerly and bold. The famous Tang Dynasty poets Li Bai and Qian Qi spoke highly of his calligraphy works.