This research wants to reveal an intermarriage political system in the Shan-Dai chieftaincy, which functioned as a large buffer zone between China and Southeast Asia. The Shan-Dai people have identified themselves as the Dai (Tai), sharing the same Dai identity and Theravada Buddhism tradition. There has been a long tradition of intermarriage within an endogamic class among the Shan-Dai chieftains. Their political authority should have been identified by the Chinese and the Burmese courts, but was mainly authorized by the Chinese imperial central governments. The Ming and the Qing courts required the Shan-Dai chieftains to provide a patrilineal genealogy, a testimonial report provided by all neighboring chieftains and signed by them and a report provided by the neighboring prefecture magistrate for the succession permission of a chieftain. In order to satisfy these requirements for the succession permission of chieftains, a system of intermarriage among the Shan-Dai chieftains had been well-maintained and had guaranteed the correlation and cooperation between the chieftains.  Meanwhile, the dowry land custom in the intermarriage chieftaincies was a means of empowerment used by the side of a chieftain’s father-in-law, the parents of a chieftain’s wife. After the 1880s, along with the colonization of Southeast Asia, the shifting borders of these dowry lands have gradually become fixed into the hard borders of modern nation-states between China and Southeast Asia. This research will enrich our knowledge about the diversity of frontier polities in a historical dynamic for future comparisons of global history.