This paper discusses two types of accents between two Chinese dialects, Taiwanese and Mandarin. The Taiwanese accent of Mandarin is referred to as Taiwanese-Mandarin, and the Mandarin accent of Taiwanese is referred to as Mandarin-Taiwanese. In this research, I establish two corpora and propose a marking-based model of accent formation, which considers universal marking a key to the emergence of accented forms. An accent occurs when unmarked forms emerge to replace some marked forms of the target language (L2). The speaker encountering an L2 constraint ranking may build his/her own ranking, which may or may not be identical to L2. In terms of Optimality Theory, a constraint in L1 may be promoted or demoted in the accented L2, and constraint mobility operates to achieve the unmarked.