永泰城位於騰格裡沙漠南緣，其建於西元1608 年，維持著相對不錯的居住人口與生存環境，但在西元1969 年前後永泰卻突然衰落。本文借助該區域過去三百多年的PDSI 指數和重建降水序列，得知永泰的衰落非受嚴重乾旱氣候所致。另一方面，根據文獻和實地調查，永泰的興盛源於當地合理的水利系統，在此基礎上，當地人在沙漠旁建造了一個頗具規模的「生存家園」,而其衰落源於當地人口遷出。本文結合當地文獻、實地考察、自然地理去探索歷史時期永泰的興廢原因，得出了兩個關於騰格裡沙漠南緣人與環境關係的結論：一是人與沙漠環境的關係很複雜，不是簡單的“沙進人退”，氣候變化也並非是所有“人沙關係”的主導；二是合理的人類活動能在沙漠邊緣一定程度上遏制沙漠化擴大，而人類活動一旦突然退出某個區域，是極可能引起當地沙漠化擴大。

Located in the southern border of Tengger Desert, the Yongtai ancient city which was built in 1608 A.D., had been maintaining favorable resident population and living environment. But around 1969 A.D., the city suddenly declined. This article, by referring to the PDSI index and the reconstructed precipitation series of the area for the past 300 years or more, comes to the conclusion that the decline of Yongtai was not the result of severe dry climate. Furthermore, according to literature and field survey, it was thanks to the rational local water resources system that Yongtai could prosper. On this basis, the local people had built a ＂Home for Survival＂ of considerable size near the desert. The moving away of population was precisely why Yongtai declined. This article, by exploring the reason for the rise and fall of Yongtai in history by combining local literature, field surveys and natural geography, has come to two conclusions: First, the relationship between human and desert, which is not simply ＂locals retreat behind a desert has advanced＂, is complex, and climate change is not the dominating factor of all ＂human-desert relationship＂. Second, rational human activities in border areas of deserts can, in some way, curb the expansion of desertification. The getting out of human activities suddenly from a certain area will, in all likelihood, lead to the expansion of desertification of the local area.