兩漢主要災異學說之中，以洪範五行傳學說影響後世最深遠。尤其劉向、劉歆父子自撰著的《洪範五行傳論》，經班固匯整取捨後，成為歷代正史災異紀錄的體例。甚至影響了後代學者對於災異分類的認知。學界對於向、歆父子的研究，主要集中在政治立場及文獻整理的貢獻上，鮮及二人災異學說體系異同的精細分析。本文主要探討劉向災異學說前後期之演變。 就《漢書》所見材料分析，可以看出在《洪範五行傳論》撰作之前，劉向主要沿襲董仲舒春秋公羊災異學說的主要看法與原則；撰成以後，其內容的確影響到其後奏疏封事之運用材料與詮釋法則。因此，《洪範五行傳論》之撰作可稱為是劉向災異說轉變之分水嶺。

Among the Han theories of anomalies (zaiyi), the one constructed in the Hongfan wuxing zhuan proves to have the most enduring influence in later times. Thanks to the admirable compiling effort of Ban Gu, the Hongfan wuxing zhuan lun, written by Liu Xiang and his son Lui Xin, even become the paradigm for later days’ writing of the records of anomalies. Previous studies on Liu Xiang and Liu Xin, however, have focused on either their political views or their contributions to collecting and assorting literature. Little attention is paid to their theories of anomalies, not to mention their differences in this regard. This article looks at the changing development of Liu Xiang’s theory of anomalies. It argues that the development went through two distinct phases, and that appearance of the Hongfan wuxing zhuanlun marked the transition as well as a significant change in Liu’s theory.