Framed from positioning theory and dynamic systems theory, the paper reports on a naturalistic study involving four Chinese participants and their American peers in an intercultural asynchronous computer-mediated communication (ACMC) activity. Based on the moment-by-moment analysis and triangulation of forum posts, reflective essays, and retrospective interviews, this study charts out participants' positioning trajectories and identifies five discursive practices (pronouns, epistemic phrases, evaluative phrases, emoticons, and posting style) as control parameters of participants' positioning systems. The study also reveals that positioning in ACMC is multiple, emergent, and contested, defying preconceived roles and identities. Therefore, the success of ACMC can be attributed to the participants' ability to make sense and make use of discursive practices to negotiate positions and achieve positioning alignment. The pedagogical implications of positioning interrogation and positioning intervention in ACMC are also discussed.