My paper examines Chinese geographers’ effort to situate Xinjiang, the Muslim frontier of the Qing empire, in an international context in the latter half of the nineteenth century. In the wake of the Opium War, a few pioneering scholars, such as Wei Yuan, turned to foreign geography. My paper argues that their geographical studies not only shed new light on the Qing’s relationship with other countries, but also reshaped the prevailing perception of Xinjiang. Before the Opium War, only a few territorial officials had vaguely realized that as an empire with colonies and ports around the globe, Britain could threaten Qing’s rule in Inner Asia.The post-war geographical studies propelled the Qing policy makers to acknowledge the British encroachment into Inner Asia and that Xinjiang was the empire's “fence” that they could not afford to lose.