The traditional use of allusions (用典) was to form an analogical relationship between different objects or events, thus bringing about associative meanings. The use of allusions in multi-style poem (杂体诗) writing was to cut off and reconstruct the relationship between the signifier (能指符号) and the signified (所指意义) of the same object or event, so as to produce an entirely new meaning. The poets in the Song Dynasty for the first time consciously realized the linguistic mechanism concerning the use of allusions in multi-style poem writing in which words and expressions should be used with their literal meanings to express metaphorical meanings (“字则正用、意须假借”). And they made widespread use and innovation of this mechanism at the levels of various textual units like words, sentences and discourses. Huang Tingjian (黄庭坚) was the representative poet of multi-style poem writing. From the perspectives of writing practice, method and logic, to cut off and reconstruct the relationship between the signifier and the signified in the texts with allusions was also the core mechanism of Shangu poetics (山谷诗法) called “Touching Iron and Turning it into Gold”, together with its related means like paraphrasing (换骨) and re-writing (夺胎). Paraphrasing was to cut off and reconstruct the relationship between the signifier and the signified in the texts with allusions at the levels of such units as words, sentences and discourses. Re-writing was to extend or negate the newly-gained meanings by paraphrasing, and form a reflective thinking (反转思辨). In his Canglang Poetic Critique (《沧浪诗话》), Yan Yu (严羽) referred to “writing a poem with words and expressions (以文字为诗)” as the treatment of the texts with allusions by paraphrasing, to “writing a poem with discussions and commentaries (以议论为诗)” as a reflective thinking about paraphrasing caused by re-writing, and to “writing a poem with learning and talent(以才学为诗)” as a prerequisite for the reserve of the knowledge of allusions commonly possessed by paraphrasing and re-writing. Judged from the positive point of view, “the linguistic orientation” of Shangu poetics was a new path opened by the Song poets under the influence of the linguistic mechanism concerning the use of allusions in multi-style poem writing, in which they broke away the tradition of Tang poem writing and moved to modern poem writing.