 He was from a prominent aristocratic family, with his grandfather Zhao Yin's having served as a chancellor during the reign of the late Tang emperor Emperor Xuānzong.Zhao Sun's father Zhao Guangyi, as well as his uncles Zhao Guangfeng and Zhao Guangyin all served in the imperial government in the very late Tang times, as well as during Tang's successor state Later Liang.In 908, Later Liang's emperor Zhu Quanzhong sent Zhao Guangyi and another official, Li Yinheng, to bestow the Later Liang vassal, the warlord Liu Yin, the titles of military governor ("Jiedushi") of Qinghai (清海, headquartered in modern Guangzhou, Guangdong) and Jinghai (靜海, headquartered in modern Hanoi, Vietnam) Circuits.