The Sutra of Mutability, also known as Sanqi Jing, was preserved in both Khara Khoto and the Dunhuang Library Cave. Among the Khara Khoto documents collected in Britain, there are a few fragmental manuscripts in the Tangut language, while among those collected in Russia, there are several Chinese versions.The recent publication of both of these collections has provided evidence for better understanding the differences between versions and the circulation history of this sutra. This paper interprets the Tangut texts of The Sutra of Mutability kept in Britain, namely Or.12380-3700 aRV( K.K.II.0258.m), Or.12380-3700 b( K.K.II.0258.m) and Or.12380-3700 bRV(K.K.II.0258.m), examines the format and contents, compares the Chinese versions from Khara Khoto and the Dunhuang Library Cave, and discusses the practical meaning of this sutra for Buddhist history and culture.