By using literature analysis to study the historical materials and scholars in this field, combined with some relevant archaeological discoveries to support our views, this paper answers an important but controversial question in the literary and historical studies of Tang Dynasty. Since the 20th century, due to the significance of the research on Suyab of Tang Dynasty and the Four Garrisons of Du Hu Fu of An Xi , and the relationship between Suyab and Li Bai, much controversy in the academic community of Suyab of Tang Dynasty and the Four Garrisons of Du Hu Fu of An Xi has arisen. These pendent issues include the problems about the number of towns named Suyab, their locations, when the Four Garrisons of Du Hu Fu of An Xi were established, when and how many times they were respectively established or abandoned, and which one of Yanqi and Suyab was established earlier, etc. The fact that the relevant documents are not clear enough and that the ancient scholars' understandings are different lead to the diverse views of contemporary scholars and the pendant problems. This paper makes a literature review of the last century, combined with the archaeological findings along the Suyab River from 1900s to 1980s, and concluded that today's Ak-Beshim site, 8km southwest from Tokmok in the Chui River valley of Kyrgyzstan, is the right site of Suyab, one of the Four Garrisons of Du Hu Fu of An Xi in Tang Dynasty. Meanwhile, due to the lack of solid evidence, new historical materials, and adequate knowledge of the political and military circumstances of Tang Dynasty, the arguments for “Two Suyabs” or “Four Suyabs” in the last twenty years of 20th century and the first ten years of this century are untenable. At the same time, there are arguments about the establishment, abandonment, alternation and many other aspects of Four Garrisons of Du Hu Fu of An Xi, for example, they were abandoned or reestablished for three times, four times, five times and six times. After sorting out relevant documents, this paper has identified three periods of establishment and abandonment based on the degree of determination to present a comparatively clear picture of the relevant issues. Firstly, the identified periods are: abandoned in 670 A.D., reestablished in 679 A.D.; abandoned in A.D.685, and reestablished in A.D.692. Secondly, the roughly identified periods are respectively: reestablished in A.D.658, and abandoned in A.D.678. Thirdly, the first established time of Four Garrisons of Du Hu Fu of An Xi was in 648 A.D., and the first abandonment time was in 651 A.D. Moreover, there was a reestablishment effort at least in the late 675 A.D. The Four Garrisons of Du Hu Fu of An Xi were abandoned thoroughly after the rebellion of “An-Shi” (An Lushan and Shi Siming, two rebel generals in High Tang Dynasty). During the five establishments and abandonments, Suyab and Yanqi were replaced by each other twice: Firstly, there was Yanqi in the Four Garrisons of Du Hu Fu of An Xi without Suyab, but was replaced by Suyab in 679 A.D.. Secondly, Suyab was in the Four Garrisons of Du Hu Fu of An Xi for forty years from 692 A.D. to 719 A.D., but it was replaced by Yanqi in719 A.D. due to the request by Tang Jiahui, the military commander of the Four Garrisons of Du Hu Fu of AnXi.