There is a large lacunae in Asian military history on the transfer of Chinese gunpowder technology to Southeast Asia before the sack of Melaka by the Portuguese in 1511.This research focuses on two issues in Sino-Vietnamese relations and Vietnamese history with respect to the spread of Chinese firearms.The first issue between China and Viet Nam is who borrowed gunpowder technology from whom.The second issue involves the driving forces behind the external expansion of Dai Viet，during the fifteenth century，including both the well-known episode of the fall of the Cham capital，Vijaya，in 1471 and the little-known “long march” of Dai Viet，troops to the Irrawaddy River between 1479 and 1484.This research approaches the issue from a technological perspective by taking military technology into account.It argues that Chinese-derived gunpowder technology played an important role in Dai Viet southward and westward expansion in the late fifteenth century.