Idiom variation is a ubiquitous linguistic phenomenon which has raised a lot of research questions. The past approach was either formal or functional. Both of them did not pay much attention to cognitive factors of language users. By putting idiom variation in the framework of linguistic subjectivity, we have offered a new perspective in the studying idiom variation by giving due consideration to the cognitive factors underlying the use of idiom. As a grammatical unit with idiosyncratic features, idiom is pervasive in language and it performs special function. Variation of idiom performs pragmatic functions by conveying extra meaning. There are underlying cognitive motivation for idiom variation. By putting idiom in the theoretic framework of linguistic subjectivity, we can say that idiom variation can be regarded as the results of people's subjective choice to achieve the expression of people's stance and affect.