This is a historical study of the city-port Quelang(雞籠) and Tamchuy(淡水). From A. D. 1400 to A. D. 1700, these two ports rose as an entrepot of the East-Asian trade, and finally declined in the second half of the seventeenth century. Employing the chinese, spanish and dutch archives, I argue that the ebb and flow of these two ports were influenced by the external cause. According to the development of external trade and politics, the early history of Quelang and Tamchuy could be divided into three periods: (1) Sino-Ryukyu tribute trade period, (2) smuggling trade period, (3) external interference period. Through a case study of Quelang and Tamchuy history, this paper seeks to explore the nature of the city-port history in the maritime trade of East-Asia.