Zheng Tai was Koxinga's clansman and elder cousin, and he handled the money. As treasurer he controlled the fleet's trade and its coffers; the revenue of the Zheng ships sailing to Japan and Southeast Asia passed through his hands, and part of the silver was kept on deposit in Nagasaki.

In 1662 Koxinga, in Taiwan, learned that his heir Zheng Jing had fathered a child with a wet nurse, and ordered the execution of Zheng Jing, his mother Lady Dong, the nurse and the baby. The order went to Zheng Tai, who was holding Kinmen and Xiamen. After consulting the Xiamen commanders he refused: they killed the nurse and protected Zheng Jing and his mother. Koxinga died that May.

It did not make him Zheng Jing's friend. After Zheng Jing crossed to Taiwan and defeated the faction that had backed Zheng Xi, he found letters between Zheng Tai and that faction and concluded that Zheng Tai had been keeping a foot in both camps. In 1663, back in Xiamen, Zheng Jing lured him in and detained him, and Zheng Tai hanged himself.

After his death his younger brother Zheng Mingjun and his son Zheng Zanxu took their men and ships over to the Qing. The silver he had left in Nagasaki became a debt that Zheng Jing and the defecting Zheng relatives fought over for years.