With the rising fever of going abroad and studying abroad, more and more candidates have joined the ranks of the International English Language Testing System (IELTS). IELTS oral test examines candidates' ability to communicate in English in real context. Based on the theory of complex dynamic system, this study tracks the dynamic development of Chinese learners' oral fluency in IELTS, and explores the interaction among complexity, accuracy and fluency by using mobile correlation technology. This study shows that complexity and accuracy are in a competitive relationship at the initial stage of the study, and gradually turn into a supportive relationship at the later stage, that is, they develop synergistically, which proves the comprehensive characteristics of complex dynamic system theory. Oral English development is complex, dynamic, multidimensional and sensitive to initial values.