Abstract: Shi Xi, a lost essay catalogued in The General Survey of Literature and History in Collection of Zhang’s Writings printed by Jia Ye Tang was not lost. It was actually included in The Complete Works of Shi Zhai printed by the House of One Hundred Thousand Books. This essay, first discovered by Zhou Zuoren in the above codex in 1942, was published on the first page in the 2nd volume of Journal of National Compilation and Translation Hall of North China in 1943. However, it was not widely appreciated because of the Japanese invasion, and the discovery did not attract the attention of the academic circle at that time. Now The Complete Works of Shi Zhai by the House of One Hundred Thousand Books is stored in the National Library of China, and Shi Xi is in the fifth volume. Nevertheless, Shi Xi is not the first draft of “Zhi Nan”, the internal chapter of The General Survey of Literature and History, as Zhou Zuoren’s epilogue said, but the first draft of Gan Yu. A comparative textual study of 16 ambiguous sentences in Shi Xi and Gan Yu assumes that Zhang Xuecheng adopted different ways to revise his works with deletion and polish. Moreover, the study also reveals the changes in Zhang’s academic thoughts and his state of mind.