1607年8月利瑪竇與徐光啟間關於西方水法的對話，導致日後熊三拔撰說《泰西水法》，其中第五卷係由徐光啟演說〈水法或問〉，本文擬探討此卷的歷史意義與影響。筆者發現，在《乾坤體義．四元行論》中，利瑪竇將朱熹開始經學傳統中的問答體「或問」，沿用到處理士人對五行與四元素間的疑難與問答。徐光啟演說〈水法或問〉反映包括徐光啟在內士人與熊三拔間關於水理的疑難與問答，其歷史意義在於他成為首位中國士人在刊刻作品中，採用四元素說來拆解占星與五行說相關的術數。在《則草》與《格致草》中，熊明遇在某些小節名稱中使用「演說」，並大量引用與改寫〈水法或問〉內容，反映他受徐光啟的影響，並將之擴延到諸多與星占有關的現象上，進行自然知識考據的省思。質言之，筆者發現徐光啟演說〈水法或問〉補上了耶穌會士作品與熊明遇對中國傳統占星氣加以省思間遺失的聯結(missing link)。 In August of 1607, Matteo Ricci talked with Xu Guangqi about western techniques of water control, which led to the publication of the Taixi shuifa (Western Methods of Water [Control]) written mainly by Sabbathinus de Ursis, in which Xu Guangqi was responsible for 'extensively explaining' (ya-nshuo 演說) its fifth chapter (juan 卷), entitled 'Questions concerning the methods of water [control]' (Shuifa huowen 水法或問). This paper aims at exploring this chapter's historical significance and impact. From the questions and answers of Chinese and Western literati featur-ed in the chapter, it becomes clear that Xu Guangqi was the first Chinese scholar who adopted the Aristotelian Four Elements Theory to criticize the traditional astrology and divination techniques of the Five Phases (wu xing五行) theory. In turn, Xiong Mingyu 熊明遇(1579-1649) was influenced by Xu Guangqi's 'extensive explanations' found in the Shuifa huowen. In his Ze cao 則草and Gezhi cao 格致草, Xiong not only used the term 'extensive explana-tions' several times but also quoted or paraphrased a considerable portion of the contents of the Shuifa huowen. Furthermore, he extended Xu Guangqi's approach to a number of phenomena related to astrology, thus advancing the understanding of Western natural knowledge in China. In sun, this paper claims that Xu Guangqi's Shuifa huowe-n provides the missing link between Jesuit writings and Xiong Mingyu's critique of traditional Chinese astrology and divination.